For juvenile boas you can feed every 5 days. I wouldn't go any closer together than that. You can keep them on that schedule till they're about 6-8 months old. And yes, you can feed two prey items at a time, I've done that with mine. Especially when they're at the point where the next size up prey item is too big, but what you've been feeding isn't enough. Boas are very good about not over feeding, so offer a second item, if he doesn't take it, he's had enough.
And J32A2 has a point, rats are meatier than mice, so if you can get him on weaned rats, or hoppers, your hogg will bulk up faster.