but isn't 6'8 too small to train a centre?
above 2m the training speed is ok, so i didn't worry about his size.
and what potential should i be looking for?
i would look for starters or better, i would tend for star and allstar potential and some extra skill from the beginning then a weaker player with higher potential - but in this case you could have different opions. A starter player had enough cap to develop, to help you for a long time but potential is also considered when you sell people and for this i don't know if you could make more money with them in comparision to a slightly better player wihtout that much potential.(hopefully i don't conduse with that, i believe someone could say that with better words, and maybe even more knowledge)