You won't get any value out of a bulb mode without a tripod anyway. For that, btw, if you're serious I'd recommend having a look at Really Right Stuff... they have a new tiny tripod that looks like something designed for ultralight 'packers, but that's robust enough for even 4x5 and big, honkin' lenses. :)
Don't bother with a big dSLR... look instead to the Nex and micro 4/3 platforms. You can get Leica and Olympus lenses for the micro 4/3, and Sony (both new and re-badged Minolta) lenses as well as Zeiss lenses for the Nex, plus the growing bevy of Sigma, Tamron, and Tokina lenses...
I think you're probably making a good choice, Panasonic stuff is pretty solid. :)