#2
Most people prefer desktops, not to say you cant use a laptop it's just easier to have a central station to record.
No means maybe
#3
I'd go with a desktop if you're doing serious recording, like full projects with a bunch of tracks. It'll eat up your laptop's memory and slow it down hardcore.
#4
there was recently a thread about this. the assumption is that a laptop will be more limited, in a large part due to the 5400 RPM hard drive. also, you typically have to pay more to get a similarly spec'ed laptop as opposed to desktop. for any serious recording, i would highly recomend a desktop. if you are more into recording occasionally and just for quickly getting down ideas or something, laptop is fine.
#5
Desktop, since the sound cards are not that good on laptop, also you can get a soundcard that was designed for high quality recording.