Once you get access to the full Broken Valley, there are a couple places you can go that would be easier than the area around Lovis' tower. From where you meet Talana, head east along the mountain to clear some goblins, as well as west and then north up a mountain trail. Both goblin areas have an entrance into the derelict tunnels.
You get the battle tower in the high teens to low twenties for level. After you finish most of Broken Valley you can more easily do Maxos temple (the final opponent is using level 15 skills, so would be easier to deal with if you were at least close to that level).
After that you can get to Sentinel Island, where there are some quests to do and areas to explore before you can take over the battle tower (the island is a little smaller than the starting section of Broken Valley).
Your first encounter on Sentinel Island you can mindread to go up a level, so the higher level you are (I made it to level 22 in the fjords) the more of an experience bonus that will be. You don't need to get to a high level, but it would be better if you got to a new level before entering, to get a full level bonus.
Ranger Strength is worth it, IMO, especially early in the game. Playing another ranger, maybe by the time I could put 4 or 5 skill points into Way of the Ranger I wouldn't give as high a priority to increasing Ranger Strength, but until then Ranger Strength helps your base damage and doesn't have any cooldown periods (and there are enough skill points to invest in both). When you get the battle tower you will be able to unlearn all your skills, and can reinvest the skill points (the cost for doing this doubles each time you do so), so you don't need to worry about early game skills becoming useless once you get higher level ones.
I did not invest in Wisdom, but did keep any items I found with that bonus, to equip when turning in quests. By the end of the D2:ED section of the game I had +8, and in FoV on level 42 I can get up to level 14. There are opponents in FoV that respawn, so that kind of eliminates the need for Wisdom (or Mindread, though I did max that skill just before the end of the D2:ED section of the game).
A little bit of strength would help with your melee resistance (early in the game there are opponents that are going to get close) and HP regeneration. If I wasn't planning on doing some melee combat when I started my current ranger I don't know that I would have gotten my strength up to 20, but I don't consider those points wasted, either. I'd have to start another ranger to tell for sure, but I think 5 or 10 points might be enough to help at the start of the game, until you begin getting equipment with better resistance ratings and jewellery with HP and HP regeneration bonuses, etc.
