I can't figure out how alchemy works. Is archery important? I believe it would be useful in case of a Dragon raid, right? I haven't touched a single bow-and-arrow yet.
I can safely say NO to all of them. I did not use any of the magic tech. save for restoration and enchantment nor archery skills. I specialised in the warrior class, improved ALL of the combat skills to level 100 and kicked arse! Fret not, you will level up gradually and steadily.
You think a frost troll was bad? Try provoking one of those giants herding a bunch of mammoths and they'll rape you left, right and center!