I don't think it is really known how much effect playing less than 48 minutes has on training. It could be that he would get 20/48 as much as someonew who plays more than 48, or it could be less than that. You really ought to have no trouble training 4 players at C/PF, and be able to get 1 or 2 others "some" training.
I don't think his size would be a problem at SF. For example, his jump shot being respectable means that his jump shot "is respectable" not that it is "respectable for someone who is 7'0". Similarly, his rebounding isn't "awful for a big man", it means that a "6'0 guard with inept rebounding will easily out rebound him". On the other hand, his height will make a difference in training, and so he should be able to improve his rebounding faster, but his jump range slower.
You could train C/PF/SF when you train inside shooting and inside defense and play him at SF, but he really needs rebounding, so perhaps you could figure out some way to get him more time a PF during weeks that you train rebounding.
I think his age would make him sellable. Perhaps training his inside shooting up to respectable might help his market value, so that a buyer might overlook his lack of rebounding. On the other hand, I might skip over a PG who had that low of rebounding.