I don't know about the maximum number of players in a guild, but I read on the EQ2 updates that SOE nerfed the Shadowknight and Paladin horses so that they only give a 10% speed boost, which makes them, to my understanding, the slowest horses in the game.
I'm really disappointed with that, because I plan on becomimg a Palading and I already have the J-Boots that came with the Pre-order, so a 10% speed increase is nothing to shake a stick at. It will be nice though, to ride a horse for aesthetic purposes.
Xczaria
Teir'Dal Crusader
Neriak Server