JS to 30 and capped SF ready, it's the easiest way. For sure easier than changing every week between IS/ID/RB. JS is very easy training, You can use guards or wingmen slots, player can play on three different possition, You can try to cap 6 players at the same moment. If player is small then JR trained to 15 could be helpful, if players is tall then RB to 15. It will be fine if OD and ID aren't black at beginning.
"Classic built" means only what we want so it doesn't matter. If we can train C in three skills we can train SF only in three skills as well (JS/JR/RB, or OD instead of RB or ID instead of JR). Of course we can train 4 or 5 of mentioned skills.
Negative elastic effect doesn't exist (the same as positive - both are neutral).