I am really not sure "exactly" what skills make a good sf
Everything depends on tactic that you play (If you play 2-3 zone, then the most important skill for SF is Inside Defense... If you play Look Inside then Diving and Inside Scoring... also Passing... For RNG that is JS and JR etc.)
The best SF is player who has all solid skills... but that kind of players is very rarely, or extremely expensive.
If you wanna train SF then you have 3 options:
1.) to train Offensive SF (JS, JR, DV... IS...)
2.) to train Defansive SF (OD, ID, RB...)
3.) to buy youth player (18y) and train him everything... if you decide this, then buy player with all skills at least average(6) and for 3 seasons you will have
good sf ;)