If you have enough spare skill points, you can add them to a skill until you can not raise it anymore, then just cancel out of it. I don't think there is an easier way of telling the maximum level, unfortunately.
Alchemy level 4 will let you make permanent potions from holy water and alchemy plants. One of the BF traders (Annabel, IIRC) teaches level 4 in act 2 and above; I'm not sure if it is available elsewhere.
