Before you can take your checkride, you must pass a written exam. These days that pretty much means going to a computerised testing center. The test is multiple choice, there are study guides available that give you the answers, and passing grade is a 70. Piece of cake.
Assuming you pass your written test, and your flight instructor thinks you are ready for the checkride, you will be signed off to take a combination oral and flight test with either an FAA examiner, or more likely a Designated Examiner who is a person who does not work for the FAA, but has been designated as having enough experience to judge whether you make the grade or not.
The length of the exams are pretty much up to the examiner. Supposedly you will only be tested on subjects called out in the "Practical Test Standards" (which you should get a copy of) but in reality most examiners use that as a bare minimum and will ask you plenty of questions that are not in the PTS. One to two hours of oral exam and an hour of flying is pretty typical for the designated examiner we send most of our student pilots to.
An example would be cross country flight. As a non-student pilot, you have to receive 3 hours of flight instruction in cross country flight before you can take the checkride. However, you do not have to be "signed off" for cross country flight the way a student pilot does. Once you have been signed off for solo flight in a category and class, you can do just about anything except carry passengers. You could technically fly cross country before receiving your 3 hours of dual cross country. I know it sounds weird, but you are a rated pilot and the FAA will let you get away with a lot that a student pilot cannot.
In general, you should plan on spending 40 hours of dual and 15 hours of solo to get your helicopter add-on. Probably 98% of our add-on students do it plus-or-minus 5 hours from that figure.
To visit each school, call them up and make an appointment to meet with the owner/president. You will usually have an easier time getting an appointment during the week, rather than on the weekend. Tell them you'd like to meet them to hear about the school, their training program, and why you might want to train with them.
Meet with the owner/president, look the facilities over, look the aircraft over, get at least the following information:
Ask to talk to a couple of the instructors. You may have to come back if they are all flying at the time. Ask leading questions, such as whether the instructor enjoys working at the school, whether the management is difficult to work for, is the maintenance good, are the helicopters all in good shape. The way the instructor answers is as important as what he/she says... If the owner told you it would take "X" hours and "Y" dollars to get your rating, ask the instructor whether those estimates are reasonable or not. Don't say the owner quoted them, just ask, "do you think I could get my rating in "X" hours for "Y" dollars?". If there is a big discrepency between what the owner said and what the instructor says, you might want to be extra careful. Ask the instructor what the pass fail ratio for the school is. Again, compare it to what the owner says.
After the tour, thank everyone for their time, leave, and write down pertinent information. Organize it with any materials they give you, and go through the same process at each of the schools you've located.
When it comes to making the final decision, first of all make sure you are comparing apples to apples. Don't price shop two schools and compare FAA minimum rates to "typical" rates. Compare minimum to minimum or typical to typical. Generally an FAA Part 141 approved school will be better organized than a non-141 school, but this is only a very general guideline. However, a non-141 school should have a syllabus showing lesson plans, number of hours, etc. I'd be wary of a school that didn't have a syllabus. If the school's insurance company doesn't waive subrogation, you could be responsible for the entire worth of the helicopter if there is an accident during training or rental. Factor in the price of renter's insurance when you determine cost of flying at that school.
Try to determine whether the helicopter fleet is being well maintained. In my book, maintenance is much more important in helicopters than it is in airplanes. There are a lot of pieces that can fall off an airplane and leave it flying. There are not nearly so many pieces in a helicopter. Of course, it can be very hard for someone who doesn't know about helicopters to determine whether the maintenance is good at a particular school. All I can say is talk with some of the current students and specifically ask them about maintenance. Look the helicopters over. If a lot of little stuff isn't being fixed, that may mean that big stuff isn't being corrected either. However, it's no guarentee either way.
Try to figure out whether this is a school which soaks it's students. I've seen many schools that take 100 hours or more for people to get a private pilot license. You will find the occasional person who really needs to take this long, but if you talk to 3 graduates and they all took over 80 hours to get their private, the school may be "overtraining" them in order to get additional revenue. A private pilot certificate should normally take between 55 hours total time for an airplane pilot to 65 hours total time for a non-pilot. If the school average is much more than that, they are probably gouging their students for extra revenue.
Most important is to talk to some of their students. This is where you will get some honest opinions about the school. Obviously you won't get much information out of a pilot who's only been flying there for a couple weeks, but students who have already soloed will be good sources of information. Ask direct questions about whether the student thinks it's a good school, who are the good instructors, is the maintenance okay, and what things are bad about the school. Obviously the school isn't going to point you toward someone they know to be dissatisfied, but even taking this into consideration, the students are much more reliable sources of information than the schools employees or the schools competition.
Spend a half hour to an hour talking with the instructor. Make sure that the two of you can get along! See how knowledgable the instructor seems to be. If the instructor spends a lot of time trying to convince you to go fly rather than talk, you may have found a guy who isn't going to want to spend the time with you on the ground preparing for a lesson that he should. Some instructors don't get paid unless the aircraft is in operation. A good lesson usually involves spending a fair amount of time on the ground talking about what the lesson will entail, how the maneuver will be flown, etc. It is fair and reasonable for the school to charge you for this time at the instructor rate. It is not fair to charge you the aircraft rate for time spent on the ground, and if there is no charge at all, the instructor will be reluctant to spend the required time on the ground. If the instructor is getting paid both on the ground and in the air, he is more likely to spend the time in your best interest, since there is no economic reason for him to prefer flight time over ground time.
Ask the instructor about his experience, both in terms of hours and in terms of how many students he has had. What is his pass/fail ratio? Is he going to be at the school for a while, or is he going to be leaving for a different flying job in the next year?
As for whether you should be looking for a high time grizzled old veteran, or a fresh CFI, that is a very difficult question to answer. More experienced instructors may be burned out, or less enthused than a low time instructor. On the other hand, a more experienced instructor will probably be able to train a better pilot in slightly less time. Still, I have met high time instructors who have been doing it for quite a few years that are just terrible, and fresh CFIs who are fantastic. There are no absolutes. This is why you need to talk to the students and recent graduates; they have the best idea of who the good instructors are, and who to avoid.
One thing to think about is that most people looking for a school will price shop based on quoted rates. But the real determining factor will be how good the instructor is. A disorganized instructor can cause you to take longer than a good, organized one. At $185/hr or more for dual instruction, it doesn't take many hours of wasted time before that instructor has cost you thousands of dollars. My suggestion is not to pay too much attention to the exact prices, but evaluate based on whether you like the people, and what their reputation is with their customers.
If you find similar resources let me know and I'll add them to the list.