I have no clue where to even begin with proper exposure, developer (I have loads of XTOL)... but that's part of the fun!
Chris, I make contrast reduction masks (CRM's) which are very similar to unsharp masks. I haven't used unsharp masks and don't remember the exact difference but I think they're a little bit denser. Anyway, here's what i do for a CRM, using my old Zone VI cold light source.
-Standardize the head's height above the baseboard (say, forcused for an 8x10 print)
-Use the same focal length lens and aperture (f5.6 for me)
-Cut the Arista lith film into test strips (under red light!). It's hard to tell the emulsion side, but it's brown instead of black. For CRM's it's emulsion up, with the negative emulsion UP and some diffusion above that (mylar should work. I use discontinued Kodak duratrans). Place some glass over this 3-layer sandwich and hold it down tight.
-make a test strip at 5, 10, 15, 20 seconds
Develop in very dilute developer to keep contrast low (I use Dektol 1 oz + water 50 oz, or Ilford Multigrade 1/2 oz + 2 quarts water) in an 8x10 tray. Develop for 1 1/2 minutes with gentle agitation (I just slide/flip the film over every few seconds).
Fix the test briefly and rinse
Place the mask on a white surface to evaluate. For a CRM it's a very light positive image with no density in the highlights.
Experiment with exposures and development times to make variations of the mask if you need to. Without the masking system you'll need to align carefully by eye and tape the mask on top of the neg (use the ruby red lithographer's tape that Freestyle photo has....it leaves no residue).
The mask, being a positive image, will have density where the negative's clearer shadows are, so it will reduce exposure there while creating edge effects that give the illusion of greater sharpness.
I don't recall the exact exposure/development tweaks you would make for an unsharp mask but the process is nearly identical.
Lynn Radeka is the master of masking and is a super nice guy. I would guess he'd be happy to answer any questions you may have.
Hope this helps!
Mark