Steve Anchell in "The Darkroom Cookbook" says 20 8x10-inch prints per liter for TF-2 capacity. That said, fixer capacity is a tricky thing, depending on throughput. If you are fixing film, use the clip test and toss the fixer when the time in used fixer is twice that in fresh fixer.
For RC prints, you can probably use the published capacity as a guide safely. For fiber-base prints you really need to adopt a two-bath fixing regime.
All of this stuff is easily located with a search here or a general search of the Internet.
As far a lifetime of fixer goes, standard is seven days in an open tray for just about every fixer I have ever worked with, six months in a full, stoppered bottle. I would assume that TF-2 would be similar.
FYI, here are the Ilford recommendations for their Rapid Fix:
6 months in full tightly capped bottles
2 months in a tank or dish/tray with a floating lid
1 month in a half full tightly capped bottle.
7 days in an open dish/tray.
Hope this helps,
Doremus
www.DoremusScudder.com
