How messy are they? Is their waste more like other lizards or similar to snakes (more solid)?
Not messy at all compare to some lizards.

I've read that you can make their food (veggies, meat or cat food mixture) ahead of time and freeze it in portions then thaw to feed... Is this correct? Also, how often do you feed them?
Here is what I do, I buy some chicken livers, collard carrots then I cook the livers and mix it in with the collards and carrots, place little portion (the size of a mayo jar) in little baggies and place them in the freezer. On feeding day I take one baggie out, mix in the calcium and add some fresh fruits. the diet is 50% greens / 40% meat / 10% veggies. I do not feed cat food, not a big fan of food with additive designed for cats, and it is actually cheaper to use the healthy stuff like chicken livers and gizzards.

I'm assuming a 4'x2'x12" cage would be sufficient.. What would be used for heating in such a cage? (RHP, heat tape, combo?) I am planning on stacking all of my cages, so I'd prefer not to use an overhead lamp for a hot spot.
4X2 is what I use however they like to bask under a light (getting heat from above versus, below), so if you stack your cages put the BTS in the last one on the top. As far as UV there is a lot of different opinions on the subject. The rumor persist that they need UV's however many people who have kept those animals for decades do not use them and have healthy thriving animals.



This cage is 4'X2'X12" and is from Chris at C-Serpents who does the Repticon Show (not sure about the next one)

If well fed, could a BTS go without food for up to a week (I'm thinking vacation here) Our pet sitter will change water, but generally doesn't feed the snakes. If this wouldn't work, that is not a deal-breaker.
Adults eat about once, twice a week at the very most. I usually offer one meal with greens and a few days later a few roaches as a treat. Younger individuals eats more often.

Also, if you have any tips on good breeders or if there's a variety of BTS to avoid, please let me know. I have not seen any breeders online yet (only resellers like LLL, etc.) and would prefer to buy from a breeder.
I know someone who has some great BTS and sometime does the Atl show.