Activity for TBD1987

Getting married end of Sept 2018 in Michigan. Currently the weather has been in the 60s. How necessary is heat and AC for the venue? They have heaters that can be rented. Also, I can't decide if I need a whole weekend or if just one day is enough for...

I have around 250 guests, venue holds 200 but there's an option to use a tent for dinner and the barn for the entertainment. What does everyone think about this option?