First of all, bimacs are not available right now. We're hoping to see some wild caught and captive bred bimacs on sale sometime in the fall.
But that's fine for you, it's going to take you at least three months to set up and cycle your tank - the longer the better.
Bimacs usually don't need heaters. In fact, we suggest that you try to keep the water temperature in the low seventies, which may be difficult in summer. To do this, I have to turn the air conditioner down and use a fan on the sump (I live in Texas). The tropical octopuses like briareus usually need heaters to keep their water temperature at 78 degrees.
Nancy
Nancy