If i buy a simple midi keyboard with one octave, pitch bend & modulator could i play a bassline with one bass sound who are assigned to one of the pad's?
Yes, but pitch bend and modulation will not affect that internal sample - the MPC2000/xl is not like a normal sampler in that respect. But you could certainly play samples using your MIDI keyboard (that's what I do)
Ya mean play a whole bassline with just one sample? The mpc won't spread that one note over all the keys like some samplers do. I suggest reading the multsampling tutorials on this site to see if this is what you're after.