If i recall while on the trans brake you will see temps rise 50 degrees every second. Don't quote me as i haven't looked at mine even in awhile while on it..
Any way hit it at the last minute possible that you feel comfortable with.
As for no coller i wouldn't even move my car with out a cooler on it.. You have made any pass's yet this year and used the brake you ight as well plan on rebuilding that tranny soon..
As for were to set the limiter that all depends on how well the car works and track conditions...
Hope that helps..