Mounts and achievements are shared over the battle.net account. You can have up to 8 WoW accounts on 1 battle.net account.

Log into https://account.blizzard.com/games and make more accounts Wow2, wow3 etc.

Consider using recruit-a-friend to get free game time. You can recruit yourself, e.g. main account recruits wow2 toon, wow2 toon recruits wow3 toon...