The 55mm is the spec for the T-mount. The T-mount adapter for your camera will take the spacing from whatever the camera spacing is, to 55mm.
Do you have a Nikon DSLR ? The spacing will be the same for the DSLR and the film SLR so you can focus using the digital camera, lock the focus and swap the bodies over.
For a tracking mount, you want film with the lowest reciprocity failure and at the moment, Fuji rules. Acros, Provia or Superia depending on what you want. For fixed tripod, you want as fast (ISO) as you can get (and tolerate the grain).
Ilford Delta 400 doesn't look too bad and it sees H-alpha (which most b/w films don't very well) but I haven't been able to find any to try. I've been using HP5+.
Orion - 30 minutes on AcrosII. Box Brownie, f/11
M42 - 10 minutes on AcrosII. WO 71mm refractor f/5.9
Southern Cross region - 30 minutes HP5+. 4x5 Speed Graphic, f/2.9 lens
