1. If you are using trichor, I'd wait a few days before retesting.
2. Yes, you probably ought to add a box of borax, and yes, you'll probably be adding borax all summer. That is NOT a bad thing. Borax is a pH stabilizer (eventually) and a moderately effective algae inhibitor, once you reach 50 ppm of borates, which will take a bunch of boxes. It's sold as Optimizer or Proteam Supreme for $3 - 5/lb
3. The TC tabs create a high chlorine zone in the pipes and filter, where the ratio of active chlorine to CC is more favorable. (That's my best guess, anyhow.)
4. The answer to what are normal levels is CYA dependent -- see the Best Guess page linked in my signature. Are you going away soon? If so, you need to buy some polyquat algaecide -- see www.poolsolutions.com/gd/polyquat.html . . . but do NOT buy the HTH label shown. I just found out HTH has been playing label games. You MUST go by chemical name.