Pulling on a vacuum costs zero work. Pushing against the atmosphere however requires work.
The force, of which, is defined by the rate of volume change. For a piston in linear motion, the cross section is constant, and volume proportional to displacement.
So the force is constant.
This can be a good way to make constant force springs; though it depends on atmospheric pressure (so, varies with altitude). It's more common to do it with compressed gas ("gas spring"), the pressure of which will increase some with compression, which itself can be a valuable feature (if the minimum volume is zero, then force increases hyperbolically with displacement, making a softer stop than a hard piece of metal, or a rubber bumper).
I don't know what you mean by vacuum vessels "in series". You can connect them in parallel, joined with a pipe; this simply increases the total volume and equalizes the pressure between them. Surrounding a rigid vessel in any other pressure (greater or lesser than what's inside) has very little effect, because of its rigidness (small change in volume for large change in pressure). The situation is different for, say, a balloon (volume varies with pressure differential, in a nonlinear manner), or a bellows or other very flexible structure. (High altitude balloons are usually little more than loose polyethylene bags; the gas expands at high altitude (lower pressure), eventually inflating the bag to full.)
Tim