Can you avoid touching the other roles? Yes, for a while. Eventually you'll max both RAV and COM and further leveling will necessarily require you to touch the other roles. Is it a good idea to avoid them? No, not at all. I think almost any experienced player would tell you that having early access to player-controllable SAB and SYN roles is a very good idea, and it's also nice to make them competent MEDs so you don't have to rely on a monster MED.
Pretty much. Multiple people told you to make sure you only took Rav with Serah and Com with Noel on large nodes. You have both so high that it's obvious you didn't listen. There's a FAQ that tells you step by step how to develop both characters' crystariums to get the highest important stats and a good spread of abilities. It's foolproof.
(Serah) STR 72 MAG 166 HP 953 ATB LV 4 COM lv8 RAV lv54 SEN lv7 SAB lv1 MED Lv14
(Noel). STR 161 MAG 70 HP 1394 ATB LV 4 COM LV57 RAV LV 1 SEN LV9 SAB LV1 SYN LV16
that looks almost exactly like mine, except Noel is a MED not a SAB....
anyway, I have a question, Is it possible to fix them at this point? and Is it possible to max out both STR and MAG for both Noel and Serah? by like, leveling both COM and RAV on the large nodes and the rest on the small nodes?