Start with flow and pressure
Add up the volume each actuator sweeps per cycle and divide by the time you have. That gives required flow. Pressure comes from the highest load case plus losses through valving and plumbing.
[Placeholder — worked example to come]
Then look at heat
Anything that is not doing useful work becomes heat. If the unit runs more than a third of the shift, plan on a cooler rather than an oversized tank.