A general question: what is the max number of players and why?
There's no maximum number of players for a PbP game, other than the number you think you can handle in one game. Obviously, more players means longer combat and other highly player-dependent events.
Regarding All giants, the options will open up a bit on adventure 2 so IF charactetrs are kept using human stats and simply scaling is not going to work.
Giving the free Feat won't work then, either, unless all the race options are Large.
Memory loss is total: they have a language and discover skills by use but that's it
Okay, this makes more sense for somewhat pregenerated characters.