The mechanic should know that. If the mechanic asks you, find another one! But for the most part what you are looking for is equal psi in each cylinder. A few PSI + or - is ok, but if all the cylinders are at 128 - 131 PSI (for example) except one that is reading 100 there is a problem. But even a not so great marine outboard mechanic should know what the compression should be.
If you are in Miami and want a T-Top you can find the guy I used on Craigslist. His ads are always the same. $600 T-Top installed. Just search the boats area for T-Top and you will see the ad. When you talk to the guy, he will show you a $600 top and a $950 top. The $950 top is so much better than the $600 top that it is not worth the $350 savings to go with the $600 advertised top. Take the much heavier duty $950 top. I am only saying this because you mentioned wanting one. Here is the ad.
http://miami.craigslist.org/boa/610749070.html
I am posting it because this is the guy I went to for my T-Top. But there are other ads for tops on the list. I can only speak for one, but it can not hurt to maybe check out some others and see what kind of work they produce and what they charge.
The joining a boat club idea is also a good idea. A very common thing for new boat owners is to buy the wrong boat. They buy a boat thinking they will use it for one use, and then find out that they either end up using the boat for something else - or the boat is not really good for the intended use. For example, lets say you intend to weekend on the boat so you want a cabin. You may find you never weekend on the boat and would rather have an open boat for more fishing space, or the cabin is not big enough and you find out after one or two weekends that you really want a larger cabin with an enclosed head or a generator and AC or whatever. Having a boat club membership allows you to try several boats and get a better idea of what you want.
Another suggestion for you is to get Sea Tow or Boat US towing insurance! You may never need it. But if you do ever need it the insurance pays for itself AND saves you a few hundred bucks the first time you use it. A $300 towing bill for a marine tow is probably below average. The insurance is around $120 or $130. So as you see, the insurance is worth it. When you get a boat, also get the towing insurance. You can obtain Sea Tow insurance at any Boaters World location (there is one across US1 from The Falls) and you can get Tow Boat US from any West Marine location. You can also sign up for either service online. In the Miami area both services are just as good, so Sea Two is just as good as Tow Boat US. So as long as you have one or the other you are good.
If you live near Coral Way and SW 87th ave there is a boating safety class conducted by the USCG Auxiliary at the West Marine store located in the mall that also has the Office Depot and CVS and Taco Bell and Burger King in it. I took my boating safety class there and it was well worth it. The classes are Monday and Wednesday from 7 - 9 PM. If this location is close to you then stop by the store and pick up a schedule. The store will have schedules for the next course, so just ask. This is the location I took my class at, and I enjoyed it very much. If this is too far from you then there are other auxiliary flotillas that conduct classes from other locations. You can search for classes here.
http://cgaux7.org/pub_classes.asp
There are two classes offered. The one day ABC class and the multiple session BSS class. Take the BSS class, as it contains more information than the one day 8 hour class.