How much variability there will be between pumps I do not know.
I suggest that you do a little experiment with say 3 or 4 pumps, running from the same supply and measure the flowrate.
If the flowrate variation of the sample is within acceptable limits you will probably be OK with the full complement of 12 pumps.
One thing which may help to give a consistent flowrate between pumps, ensure that the tubing on the inlet side of each individual pump are all the same length, and similarly that the tubing on the outlet side of each individual pump are all the same length.
As regards the switch on surge current, if it turns out to be a problem, how often will the pumps be stopped and started?
Every few minutes?
or
Started and left running for days and weeks?
If the latter case, just have several switches and switch the power to two or three pumps at a time.
JimB