Orbiter and Add-Ons
I am new to Orbiter and there are others with much more expertise. However, I think I can contribute here.
1. Not all add-ons are designed to work with the latest version of Orbiter2010, and furthermore, add-ons are not necessarily designed to work with one another. You have to be somewhat careful about which add-ons you install (makes sure they are for the version of Orbiter that you have) and also check to see whether other software is required for the add-on you are attempting to use (like an SDK or even some other add-on, or something). That said, even if you install a couple of add-ons that are for the current version of Orbiter, there is a chance that they are incompatible with one another, and may cause errors or a CTD. The only way to avoid these sorts of things is to test every add-on for stability and add them one at a time, in the order you need them.
2. For the current version of Orbiter, I would use this thread :
http://www.orbiter-forum.com/showthread.php?t=16177
and install only those add-ons listed which you determine you need. According to that thread and the community there, these add-ons are tested and known to work with the current version of Orbiter. This does *not* mean that if you install various add-ons from this list that there will NOT be some kind of other issue due to add-on - add-on compatiblity. But, if you install add-ons one at a time, and check the appropriate add-on box in the "Modules" section of the Launchpad, you can determine where a problem may have come up, and then make a decision about which add-on or set of add-ons you can actually use. Also, keep in mind that the more add-ons you add, the more your computer has to do, and this will slow your framerate down.
Anyway, the above process is now what I am doing. The point is you just can't add add-ons willy-nilly, much as one would like to = many of the add-ons are really good additions and really enhance the game and we would like to run all of them. For example, I really like AeroBrake, but that add-on is not on the list I mentioned above. If I install it anyway, I will have to do some serious testing to make sure it's compatible with the application version and all the other add-ons.