I've been considering replacing my stock battery on my five six year old Libby. This summer I accidentally drained the battery a few times

Once the really cold weather arrives I'm afraid it won't work anymore.
I would think a 600 to 800 CCA battery would do just fine. The Optima batteries are great but since I don't plan to install a winch on my Libby I can't justify the cost (over $200).
As for the headlights I doubt that they don't need adjustment just brighter bulbs. Try a comparison to another Libby.
Don't they check your headlight adjustment during the annual motor vehicle inspection? or maybe they don't do it in your state.