1. Octalink V1 109.5 mm, English threaded as noted. BB-5500 is good and relatively cheap. BB-6500 is out of production and difficult to find even NOS. BB-7700/7710 is pricey and requires routine maintainence. Any of these will work.

2. Yes

3a. All require the same Shimano or Park Octalink/ISIS bb tool. Park's newest versions are the BBT-22 and BBT-32 Both work but the BBT-22 is a bit heavier and more versatile.

3b. The 6500-series cranks have auto-extractors built into the crank bolts so, in theory, you don't need a separate crank extractor at all.
You can use a small pin spanner to remove the autoextractor collar to clean everything inside before reinstalling the crank and to be able to look and see the splines are aligned correctly before torquing the crank bolts down. A pair of needle nose pliers with small tips will work as a substitute.

4. No.