Jump shot and jump range train the fastest on guards so I would wait on that to get other things out of the way before his training dramatically slows down. OD is the most important skill in all of BB. On the national team, all guards have at least 19 OD. OD allows the guard to pressure them, block passes from going inside, affect jump shots, not allow someone into the paint and more, no other skill can make such a big difference in a game. For new trainees always start with 1V1 guards because of the elastic effect. The elastic effect says that skills lower then all other skills will train faster to catch up, and 1V1 guards is perfect for that because it trains JS DR and handling.
For promotion, the team who wins the finals always promotes and if there are still a couple of bot teams after all the champions are promoted, then the D5 teams with the highest country ranking promote.
Hope this helps!