The battle tower is on Sentinel Island, with the path leading to it in the area west of the main shipwreck survivors' camp. Initially there is a barrier blocking access until you have progressed enough with the main plot (finish off everything else on the island, and in Broken Valley, before completing the battle tower).
You got a book of magic that can control wind when you rescued the guy on the top of the pillar (near the trainer Kenneth). There is a windy spot near where you start on the island with a tombstone and three candles...
I maxed Lockpick as soon as I could, and don't regret it. Wisdom I didn't bother with, though did use a couple pieces of equipment with a Wisdom bonus. Late in the game I had spare skill points, and put some into Wisdom (next game I probably will not, especially since I'll be playing a ranger rather than a warrior, so will likely have less free skill points).
Once you get the battle tower you will be able to unlearn all your skills and reinvest them where you wish. The cost to unlearn skills doubles each time you do so, but you should easily be able to reskill 2 or maybe 3 times.
