#1
There are some things that bother me for a while

1. Do different keys sound different?(like more majory or more minory)
2. Will it matter if i use a key with more sharps rather that one with less sharps?(except for the key signature)

And some of topic. I need a not too fast yngwie malmsteen song
George Bernard Shaw


Hell is full of musical amateurs.
#4
I don't think the number of sharps/flats is that big a deal on guitar, as most people use tab to some degree anyway, and tend to think in terms of intervals and position more than note name.

If you asked me to play something with 5 sharps on my trombone, on the other hand, I'd probably swear at you. So if you start composing for other instruments it might be worth considering key sig in terms of playability as well as for the sound you want. Until then, use whatever key you fancy.