I follow the same weight rule with my BCI, but don't feed her as often as I do my balls. They have a much slower metabolism if you will, in that they put on weight and can become obese very easily. For instance, as youngsters instead of feeding every 5 days like I would a ball, I fed every 7, and then once she hit 500 g I put her back to every 10-14 days.

I also found it was easier to keep her weight at a good spot by feeding her mice instead of rats, but either is really fine for them. It's up to you what you prefer to feed.

As far as feeding inside/outside the enclosure, I've found it much easier to feed in the enclosure considering how strong boas' feeding responses are. I'd have a tough time getting my girl out of her tub and into a feeding tub, then back in, considering she's usually still on the alert the day after feeding day anyways I also found it useful to have a snake hook around just in case she decides she feels like having a snack when I want to clean her cage, just so that I can let her know it's not feeding time by stroking her with it or moving her with it if I need to.