I'm not sure I would do a biweekly feeding on your mainland. Pythons generally eat a lot more than boas and I think you would be starving him. I would feed him weekly. True you can control their growth to an extent with food intake but you got a mainland. It is going to grow to large. No point trying to avoid that fact by starving him. I'm no retic expert but I would feed him weekly for his first year and then evaluate how he looks and go from there. If he looks rather chunky, then maybe back off some. If he looks skinny give him more. If he tries to eat your face whenever you open the cage, feed him a lot more lol.
Caesar my 6 month old SD/D guy is out windshield wiping and patrolling all over at night after his 4th day. I was going to do weekly feeding with him but I might have to do every 5 days until he hits a year and then drop him down to weekly or longer. he is a pig though and has an incredible feeding response.
Thank you for the advice. yes I would feed him weekly for this first year