hey there.
I am also planning on training a SF for the next few seasons.
My trainee is 6'7" with MVP potential
from my knowledge, yes SF's bridge the gap between Guards and big men. However there are outside and inside oriented SF's.
Either way, you should train both inside and outside defense, and try to make the player well rounded, but pick an inside or outside focus.
The 6'5" is good to train his guard skills, 6'8" can be more inside oriented, almost like a PF.
And the 6'6" in my opinion, looks like he can be great all around.
So its your call, but you should know if you didnt already that there are many options for you to play around with.
personally im trying to get my SF right in the middle for the first 2 seasons, then wih whatever times left over i may train up certain spots.
Good luck.
btw: if anyone wants to shed some advice for me aswell that be great.