I have Cubase. Would I be able to create decent sounding drums for demos if I have a keyboard rather than programming them in Fruityloops or something?
Well, I have three keyboards but use the Boss 880 drum box. I have a Motif with great sounds but have not yet explored using the drums in it; thus, I can't give you much insight there--however, the Motif and its replacement synths XS models are equipped to do just about anything. You'd have to talk to a vendor-techie person to get specifics or go on line and poke around.
I still have my DX7 up and running. The battery on the DX7 still checks out up to par and I have had in a box for a couple of years. Just mounted it on a new two-tier rack. Quiklok type and VERY sturdy. Got rid of the A-frame rack and got back about 5 feet MORE of working space in my studio.
BTW: The Boss 880 has many patches with built in bass and you can change the key or turn off the bass. It rocks.
I have an Edirol PCR-300 keyboard. As well as piano keys for "sustained note" instruments, there are 18 pads for "quick hit" instruments, like drums and other percussion stuff. Works well with my synth/samplers and soundfont players. Like others have said... for drums, a keyboard with pads of some kind, or a separate pad device, makes things a lot easier.
How many keys do you want it all depends. I would look used I got a really good deal on a 49 key maudio radium because it was open box. Go to guitar center and see what they have, usually youll get lucky and theyll hve something.