I believe even for FTP games there is a critical level below which you risk people leaving before they could discover a favorite class or play style that get them hooked. Tera has 2 free slots and I played for about two weeks. Neverwinter had 3 when I tried it and I played it for about a month. WoW has a whole lot of them and I've played it on and off for several months altogether. CoH had 88 at startup and I played it till the servers were shut down. Of course, CoH was excellent in many other ways, but I might not have played it long enough to discover that if it started with two slots and I tried first with an storm controller and an energy blaster. ^_^ (No offense to either of those power sets, but you really needed to understand how the game worked to be useful with those and a few others.) So that's why I think starting with too few slots is shooting yourself in the foot - you scare away people by having them run head first into your paywall before they have enough momentum to break through.

I'd probably be happy if I saw 6 character slots free. I have no problem if people can unlock more through various in or out of game ways, but I think 6 is a decent starting point for a game that is just launching.

Free-to-play (if it has that option): Just 2 for each server.
Subscription: About 8 for each server the way it was in CoH.
Lifetime Subscription: About 16 per server.

Can buy more in the microtransaction server.
Events that give out character slots.
Making a max level character gets you a free character slot (like in Champions Online)

RHUMOBUTHOGURRO wrote:
Brackers +1
makes 9!

Bingo! *starts planning 9 characters with full background story*

I like having around 4 if you can respec your character with out to much hassel or in game cost. Otherwise 8 if it cost real money or takes to much to respec a character. In my opinion design usually is the only thing that I understand paying to redo since it doesnt effect gameplay and you picked it originally.