Hello,
I've seen hand painted / roller painting methods which have given very varying results..a good rollered paint job can easily look better than a poor spray job. But the key with any kind of painting is always the prepwork. Spraying obviously gives a more professional finish (he says, ignoring the orange peel on my own series 3..) and I think is much more satisfying BUT as I said, any finishing method is only as good as the hours, and hours (and hours) of prep. Depends how much time you want to put into it really but don't be lead by anybody saying one method is any easier than the other if you want a decent finish any way of doing it is going to take alot of rubbing down (especially between coats).
Based on my own experience of spraying - use 2K paint, no need for clear coat and hardens off really well to be rubbed down and then polished up to take out minor defects. Go for a dust coat, followed by two to three (three ideally..) full coats and then another lighter dust coat. Primer you'll want 2k anyway because it's going on aluminium. What paint is on the panel work at the moment? Alot of mine was hand painted and the paint did not mix at all, so I had to strip it ALL (bare metal respray on every panel in the end, but was easier as it was a new chassis rebuild so everything was sprayed off the vehice anyway).
Don't be scared of using a spray gun by the way, who needs a three year apprentiship to spray a vehicle!
All the best - and post pictures!