If you're buying a telescope, get the biggest aperture you can. The more light you get in, the more you'll see.
Magnification is not as important, and certainly something like 300x or 400x is utterly pointless. The more magnification, the dimmer the image, and at 300x through a little 3" aperture telescope you won't see much. Something like 50x is actually useful.
For example, I'd much rather have a pair of 12x 50mm binoculars than a 200x 50mm telescope. With twice the light-gathering capability, you'll see heaps more with the binoculars even though they are lower magnification.
I'd try to get a reflector telescope rather than a refractor, because you'll generally be able to get a much bigger aperture in a reflector. Something like a 4" or 6" reflector would be excellent as a first telescope.
That the sort of info you're after?
Oh, and stellarium is indeed awesome.
