Multi-instrument MIDI control

[circlemouth]

I have a Yamaha A3000 sampler and an Ensoniq synth. I am about to buy a sequencer (quite possibly a Yamaha QY-300...if not that, a Roland MC-50mkII...which is better? Any other suggestions for that price range?).
What I have in mind doing, since I am mainly interested in producing complex arrangements that I can control all myself for live situations, is programming the sequencer to control the sampler and keyboard through MIDI, while I am also playing another instrument and singing, so they would function as accompaniment. I may also get a Roland XP-10 (can anyone suggest another synth in this price range that is better? My Ensoniq makes a lot of crazy noises; I want another keyboard for piano, organs, and strings). If I do I want to control it also. Are the sequencers I'm looking into capable of this? How can I go about carrying this out? Thanks.
O!

[PPatrick]

I don't know if I can answer any of your questions, although I have the Roland MC-50 mk.II. It's a decent sequencer, as far as I can tell. I see no reason why you couldn't use it live to play several MIDI instruments while you play something else. I've used it mostly to record several tracks of MIDI, to be played back later as part of a mix with multi-track audio. It synchronizes well to multi-track audio, which I like. But I've never used it in a live situation --- although the mixing with multi-track audio is kind of like a "live" performance, so it doesn't seem like it would be a problem.