Nice player indeed!
What makes sense to you, depends on what you want out of this game. You just want to progress your own drafted player or do you just want to train a guy and optimize your team? You want this guy to eventually end up with 250k-300k/week salary, or would you prefer to keep it below 150k/week? You could chose to sell this guy and buy an MVP potential player for a fraction of that money and spend the rest elsewhere, and you can train him to be a great player with up to 150k salary instead of 300k. The all-time great potential doesn't give you anything besides a higher salary ceiling, so if you don't want that high a salary on your player selling him could benefit your team greatly.
You could still just keep this guy and not train him to reach 250k+ salary, if you're OK with not optimizing your resources and just want the fun of shaping this guy you drafted yourself. No right or wrong answer, just what you prefer.
About selling/relegating, do you want short term success of you're aiming for the long run? If you want to seriously train this guy, you'll have a hard time competing so it might make sense to sell your high salary players to maximize weekly profit with a lower payroll. I'm in the same situation with young trainees, but I just couldn't resist buying great players with the money available and ended up not making any profit and not winning the 'ship either, but I had fun doing so and appreciated the challenge of balancing training and competing. It wasn't best for my team long term, but it was a lot more fun this season than tanking.
About how to train this guy, do you want a unique type of player or just want the best according to current knowledge? You want a great scorer or a passer or a defender, or a blend? There are multiple ways to go about this, again this is just what your preference is. Most training plans for guards/SF's start out with 1vs1 (forwards), so that's a good way to start.
If you give some more answers about your preferences I (and others) can give you better advice how to reach your goal.