I'm not sure you CAN limit the number of times a unit is respawned using base or instant.
Are you making a coop? I like to use group respawn for coops, that way there are no more men in you group than what you start with, of course you have to leave the AI on when you start the mission with this technique.
Never made a SP mission, but seems the same concept would apply.....
For a CTF or CNH, it could work as well until you are out of respawns, then you would get plowed as you have no one on the field anymore....
Hope this helps......