Controlling 4 motors and 2 actuators with Arduino

MarkT:
Hmmm, those motors look a bit underpowered - a continuous power of 37W isn't much, so in adverse conditions they could run very hot.

Of those controllers the last two are wash-outs I think, 0.1 ohms internal resistance is too high. The first has the current ability but
doesn't have any protection circuitry - you want at least to have an over-current cut-out to prevent burn-out of motor or controller
in stall conditions - but you do get a current signal output to monitor, allowing current control in software.

The first one claims 30A, but it won't take that, the MOSFETs are 0.005 ohm, so something like 15 to 20A will be the practical
max continuous load I think before it starts to get too hot. fan-assisted cooling would help there perhaps. 20A per motor though
ought to be enough ??

It is nice and cheap to experiment with, and with only 12V there are various failure modes you won't have to worry about
so much (high current and high voltage together make robust H-bridges trickier to design. I suggest getting one of this 30A one and seeing if it performs as advertised, firstly with a dummy load like some car bulbs, then one of the prospective motors/actuators.

It should be enough for at least one of your motors/actuators

I appreciate the help! Do you think I would be able to run 2 motors in parallel off one of these if they are only going to be run for minute-long intervals with large breaks in between?