All that can work; these "Kelvans" will just have to be designed to avoid any similarities to SFB Andromedans,...
True. Pretty sure we're doing something similar anyway with all the other ships and races when compared to their SFB counterparts, so... Shouldn't be too hard.
...meaning no satellite ships,...
Use runabout class vessels. Lots of them. Some bigger, some smaller. All called "Runabouts". It'll be close enough.
...power absorbers, TR beams,...
Give them shields instead. Combine the PAs and the TRs into a Power Absorbing Beam. It leaches power from the target to do whatever the Kelvan ship would need it for. For fun, give the Kelvans the ability to "fast charge" their phaser equivalent weapons at 2x cost - the extra cost can come from a bank of batteries that can be recharged by using the PABs.
...displacement device,...
Its just a transporter with a fancy name...
...etc.
There is actually quite a lot to cover here.
Auxiliary ships can just be a mix of specialized "Runabouts" and captured Milky Way equivalents. They wouldn't have the production base to build their new empire right off the bat and would need to "borrow" some things anyway - and why scrap an otherwise useful vessel? I actually see the borrowed ships in use until the end.
A base is a base is a base. Realistically they would just be in need of a good, original model. The "guts" would be similar to their ships in terms of components and similar to MWG equivalents in amounts.
The Temporal Elevator would be tricky, but not impossible. Rename it first off. I honestly can't think of anything right now. Second, the effect does not move the base (or anything in the elevator's hex) "up" or "down" but rather just barely forwards or backwards in time. Like 0.1 seconds or something. See TNG: Time's Arrow.
Definitely want to make the models of the ships look like SFB Andromedans without actually making them look like SFB Andromedans. Something of a cross between original and an homage.
The Operation Unity campaign was done, more or less and slightly differently, in SFC3. Would not be too hard to borrow something similar while keeping it original.
I miss anything?
The Czar
P.S. It is fitting that the Kelvans appear in the episode By Any Other Name. If its handled correctly, it will be Andormedans, just by another name.