I've thought about leaving firebolt at rank 2, as well, but the jump in damage from rank 2 to rank 1 is pretty nice, although it does cost 5 more mp for a full cast (which adds up, I know.) Going from 95 max at rank 2 to 120 max at rank 1 is pretty nice.
I'll take 5 mp for 25 more max damage.
You have icebolt, though..
For potion making/herbalism.. You need to make so many hp/mp potions at earlier ranks, that you'll be overflowing if you focus on just ranking potion making. Herbalism, alas, costs about as much as a bolt spell to rank all the way to r1, and doesn't give stats well for its ap cost. For me, at least, herbalism basically ranks itself passively; I'd be getting the herbs anyway for potion making. XD
Potion Making isn't exactly what I'd consider a 'fun' life skill, though. There's no fun mini-game, and the person isn't exactly involved; if there was already herbs in the character's inventory, a trained monkey could make potions just as well as a person could. It does get profitable, but it's harder to make 100 versions at earlier ranks.
You could always rank healing to at least rank B, for healer enchants, or to rank 9 to get some ap back from the quest. Or, you could rank it r9, then reset it back to rB.
Don't forget to invite me to your potions parties, if you do go into it!