Too many aircraft?

I have a problem. Whenever I choose to fly an aircraft, I get the engine sound of the default Cessna in the aircraft I chose. . Sometimes I even get the Cessna's panel. I have a ton of airplanes in my Aircraft folder (when I click on the aircraft button to get a new airplane, it takes about 30-40 seconds for my choices to pop-up). Anyone have any thoughts on this? Thank you.

I doubt that this happens with ANY aircraft you select to fly. However, I've had the same experience every now and then.
Usually this is caused by the fact that the sounds and/or the panel are aliased to the default Cessna.

Solution: Place appropriate panel and/or sound into the aircraft or, if you're comfortable with aliasing do that. It saves you a lot of HDD space in the long run.

As to the second part of your query, having a multitude of aircraft in your hangar will slow down the selection of a particular one - I have found that this applies especially to aircraft with heavy (good) paintwork.

In the end though, this shouldn't prevent you from having as many aircraft as you like in your collection. There is also the issue of house-keeping i.e. defragging, disk cleaning etc.. I know many simmers who have hundreds of aircraft installed and this is no exaggeration.

I have to come back to the "aliasing" business. If you are not yet familiar with the procedure, start looking into it.

For arguments sake let's say you have 8 747s with Rolls Royce engines. The RR soundset may weigh in at 60 MB. Instead of placing this soundset into each of your 8 747s, you have it only once in a special, separate folder. From here you can alias the soundset to all 747s.
And so it goes with the panels as well.

Finally the textures. Lets say you have ten Posky 747 (all of them the exact same model of course), the only difference being the textures/liveries.
There is absolutely no need to have ten identical aircraft when one will do. All you need to do is add the various textures to the one aircraft and you're saving space again. I keep mentioning 'saving space' because the more FREE space you have on your HDD the faster your sim will load.

Many simmers struggle with the procedure of adding textures. The problem in most cases arise because the texture artist made a mistake in the text that has to be added to the aircraft.cfg -- it can cause a headache if you don't know what to look for but... if I can do it, anybody can

If you wish to embark on any of the above mentioned adventures, I'll be happy to assist you.