]If I get Character B1 and Character C1 to level 60, how many "grant a levels" do I get?
29 granted levels, cause you gained 59 from 1 to 60. You get 1 granted level per 2 levels gained.

Character C1 should be able to grant 30 levels to Account B - say, to get Character B30 to level 60.
B30 should get another level if he wants to ding 60 from granted levels.

Can I then take Character B30 (now level 60 due to these gifted levels), and grant 30 levels to someone on Account A?
Yes (only 29 levels though), you can grant levels with levels gained from granted levels. (hope you are with me;)

And Can I gift 30 levels from Character B1 (now level 60 due to standard leveling with Character C1) to someone on Account A?
Yep, another 29 free levels for account A.

When I've RAFed, I've leveled 3 teams to 60, and 3 or 4 to 31. That's been a lot of lvl 60 toons on the accounts at the beginning of the RAF chain.