What type of Audio Interface/Mixer will I need?

I currently have an MPC 1000 and will be getting a Macbook, a MIDI Keyboard (probably an M-Audio 61Key's one) and either a sound interface or a mixer for christmas.

Eventually I would want to connect studio moniters to the interface/mixer. However for the mean while I'm happy just using my computer speakers (which are good quality ones). At the moment they're not a necessity for me.

Would anyone be able to recommend me some interfaces/mixers that will suit what I'm doing and that aren't too expensive? (Well at least just not the very top of the scale stuff)

How many channels/ins do I need?

Many Thanks!

U will need an interface anyway. It depends on u whether u need a mixer in the chain or not. In ur case it's not necessary, or u must really hate it to adjust levels inside ur DAW with ur mouse. A mixer offers u some tweaking outside of the computer before u record.
If u do decide to also go for a mixer u can go for a dedicated interface and a dedicated mixer. U can also buy a mixer that will also function as an interface.
Do a lot of research and think through thoroughly what u want/ need. Mind that u might want to invest in something in which u can grow. And again, to some good ol' internet research on interfaces, mixers and combi's.