can you really build a satellite as a hobby project ?
Yes, there are things like cube-sats. Problem is affording the launch price. ;)
Even building a cube-sat that never leaves your desk would be an interesting hobby project, really. Non-experts would certainly learn a ton from doing so, and you'd end up with a cool conversation piece, if nothing else.
Absolutely. It's why building one is on my todo list.
Although it could be attached to a weather balloon and still be useful for scientific testing.