Buffertanks.
Industrial guideline is that a buffertank has at least 5 times the volume of the used volume per action. But that would make it very large for our purposes, so I give myself the guideline of 3 times used volume.

In a low pressure setup, the buffertank doesn't do a lot to combat freezing as it has the be in between the regulator and valve.

Ram stroke and bore.
A long narrow ram or a short fat one deliver the same amount of power, if the volume is the same.
Problem is, commercial long narrow rams have smaller inletports, and those restrict flow.
As you remark, long narrow rams are more vurnable to bending forces.
I myself try to keep stroke to a minimum, with stroke up to twice the bore (a 50mm ram will have 100mm stroke or less.)
On the other hand, that's not commercial stuff.

Amount of force on the tip of the arm.
Hannibalito 3 does about 200 kg. Hannibalito 4 goes over 400 kg. But those are Full Pressure setups.
I have seen robots with linaks (electric "rams") pushing 25 kg on the tip and win fights. Not fast, nor powerfull, but very controlable and easier than pneumatics.