Once you have the battle tower, potion ingredients are easy to get, and you will not need to worry about conserving them (you still may not need them very much, though). I tried not to use potions early in the game, but once I effectively had an unlimited supply, I stopped using food (level 1 of the healing spell was usually enough, though, so potions were mainly for healing in the middle of tough fights).
Playing a ranger I thought a fighter creature might compliment that build, but it tended to draw more opponents into a fight than a ranger/mage creature would, making things more difficult. Any advantage you have due to the Ranger Stealth skill is lost if your creature runs up to the nearest opponent.
In D2:ED playing a warrior I just automatically went with a fighter creature. I ran into trouble trying kill a couple opponents 4 levels above me (trying to level), and found a ranger head made the creature much more helpful. When I found a mage head after that I switched to it.
The experience you got mindreading the island may not have been as much as it could have been, but the difference isn't going to matter once you've gone up another dozen levels. I did as much as I could in the fjords to get to level 22 before heading to Sentinel Island, and got very little experience from opponents after that.
Playing a ranger I opened the barrel in the mirror room about a dozen times, jumped back and took out the majority of the opponents with a couple exploding arrows (getting hit many times during the 5 second cooldown, with Static Charge and retaliation auras being triggered almost constantly). It was fun seeing so many opponents die at once.
If you sell Vacca's gem before you talk to him again, you will not need to fight him (so you can complete the quest he gave you).
You can get most of the way through the battle tower (opened after you return Sassan's ring) before you need to worry about completing anything left in Broken Valley. There is a warning in-game before then. In Broken Valley entering the quarry tower can wait until later, and on Sentinel Island you have to wait to get the treasure from the boat in the tree (though you may want to use the item yourself, rather than complete that quest).
There is a set HP and mana boost per level, as well as the amount from Vitality and Spirit. Investing in Vitality early does not give any extra bonus.
