Awesome prospect; I think you are going the right way first with outside training... I am training a 6'6 guy and 6'7 guy in OD and although it does take longer it really is worth it. If you can get your guy up to Prolific in his first 2 seasons then whatever you decide to do from that moment on is just going to make him more and more valuable. IF you only plan to get him to strong then bear in mind he won't likely be able to hold down the PG slot at higher leagues and it will make him look very ordinary on the TL if you decide to sell.
The question you have to answer is are you ready to commit to OD. If you do then this guy could have a very long career with you.
Good luck!