So you are suggesting to keep the 6'5" guy so that when you stop being able to afford the 7'0" guys, you can buy some gaurd trainees and continue training the 6'5" guy? Is that right, or did I misread what you wrote?
Thats what Im suggesting.
Assuming each 7ft guy goes to 15k salary (end of season 1) 40k salary (conservative end of season; Sell 1 7ft guy (saving 40k salary) Buy 2 x 5-7k guards and train OD/PA/DR anything really that wont really make the 6'5 guy that much more expensive.
At this time he'll have a great Center, a decent SG/SF(the 6'5 guy) and 2 other trainees as well as whoever he was fielding originally. He could be in good position to promote at this stage (much more chance than with 3 centres) and with luck he'll be able to hang on to all his players from here on in.
How do you see his team evolving with 3 big men only? At what point can you see him improving his guards (understanding that guards are the most expensive to buy off of the Transfer list.)