Turning tournament mode on and off is a backwards way to get what you want. By definition, tournament mode stops the map cycle and will reset at the end of the timelimit on the same map. There is no way around it.
What you want to do is turn auto balance off (which tournament mode does for you)
mp_autoteambalance 0 //can't remember the exact name of the cvar and don't have access to my config files.
If you set this cvar to an extremely high number like 30, then teams will not be scrambled before a map change.
tf_arena_max_streak 30 (max wins before team scramble)
There are a couple ways around having a bench. The first is this plugin for sourcemod
http://forums.alliedmods.net/showthread.php?t=76466 which allows you to set your max team limits and if you set it to your maxplayer/2, there will never be a bench.
This should solve your bench issue as well.
maxplayers 32 //to increase the team size to 11
sv_visiblemaxplayers 22 //
Hope that helps.