Depends on how many MFCs you plan to control, and whether you want to do more than just change the setpoint.
Many of the NI multifunction DAQs have 2 analog outputs. Some have
none. If you want 4 analog outputs I think you will need an AO-only
board.
The good news is that MFCs are slow enough that pretty much any
sampling rate will be OK. 8 bits might be adequate precision and 12
bits should be plenty.
