1. Thermostat probes go outside the tub, between the UTH and the tub itself.
Larger tanks that use RHP's, or heat lamps, can have a probe, or probes, in the tank, but hanging on the wall, not were they can be sitting in spilled water, waste matter, etc.
2. 80F is fine for the cool side, but please, get an IR Temp gun so you know for sure. Do not rely on thermometers that take air temps.
3. You want to feed 1X a week a prey item that barely makes a dent. Boas are incredibly efficient and should be slow grown.
How old is this guy and how much does he weigh? Is a hopper (mouse) about the size of him at his biggest girth?
4. DO NOT FEED in separate container(s). This is a) a myth that it helps prevent bites in the tank (unless all you do is feed and never take out the snake) and b) you are more likely to get bit by a food hungry boa trying to move it in food mode.
As mentioned prior, hook train your boa, feed in the enclosure, and you will have likely zero issues. A 6FT male BI will cause a lot more damage than a 4ft BP in a food response bite. Boas are known to stay in food mode for days.
I commend you for asking good questions, but please take the advise of experienced boa keepers on here (not just me).