I'm not sure what you mean by ammo going stale. In any event, I'll try to answer your questions. The magazine spring will not lose it's tension or "springiness" by storing it with it fully compressed with ammo for long periods of time. In fact, there are accounts of people storing loaded magazines for multiple decades where they still functioned perfectly. A spring loses it's springiness from being repeatedly compressed and decompressed many many times, not from resting either in the compressed or decompressed state.
I have a Glock that I've owned for almost 20 years. I tend to use the same magazine most of the time. It will sit fully loaded for many months, then I'll take it out and shoot the heck out of it and remain fully loaded for many more months sometimes. It still functions perfectly. The bottom line is that you don't have to worry about magazine springs unless you are shooting competitively and dumping thousands of rounds down range every few months.
Now to your other question - revolver or semi-auto. Get the one that you really want - you can learn to shoot either, and there is no rule that you must start out with a revolver. However, if you are going to keep it for home defense or self defense and have no real interest in shooting for fun right now, then I'd recommend a decent revolver. They are simpler to use - pull the trigger and it goes bang.