Hi trialus,
Do what YOU think is the best for your Ranger
And if you wish to read my suggestions, go on and read this post
1) I first of all put all statpoints into Vitality, all of them the first 5 level-ups, really.
Playing mostly like a Ranger (using a bow) I haven't had any problems my dexterity was low and besides: you can find, make or buy potions for temporarily increase your dex. (or strength, intelligence or full resistance!) ... but there're NO potions to increase your Vitality

only Healing potions, but with a low vitality in a difficult fight you're stone dead before you noticed it

...
Later in the game I decided to go more for Magic Damage, so I begin to put statpoints in Intelligence (I began like a Mage with Fireball as starting skill!) and search for equipment that boost above all Vitality, Spirit & Intellingence or Magic Damage (worn the full Armour Set 'Defenders of Aleroth' boost greatly "Magic Damage", among other great boosts!).
If you wish to only increase your Ranged damage, put points in Dexterity & for Melee damage go for more Strengh
2) I too like Stun Arrows because it give me more "time" to figth or run away

... I'm a "slow" player, that's why I love that skill. Now I've 2 points in this skill, but 1 point is at least handy. and maybe 1 (or more) point in Ranger Suprize combined with Stun Arrows AND after that using the Warrior skill Rush Attack ... hmm ... it's a great & funny way to kill a strong fighter more easely or finishing of a Ranger that using poison arrows at you, very dangerous!! (bandits!) But using Ranger Suprize, Stun Arrows and after that Rush Attack the "bandit" is stone dead

!
I put NO points in Rush Attack, but only find/buy a Bracelet (or whatever) by a trader with this skill on.
At least 1 point in Ranger Stealth can come in handy for sure!
3) I think it's possible, especially if you put points (like I do) in
Intelligence :
- a) if you wish to change to a melee fighter you can search for the best melee weapon that have the highest Magic Damage (and other stats you like most),
- b) if you wish to change into a Mage your only have to re-skill and go for Magic spells. But beware: don't go to the "battle field" without any melee weapon
... especially in the beginning you're searching your favorite Mage type and you're not strong enough to survive without any melee weapon (or bow). It Is possible, I've read on this forum someone playing the whole game as a Mage without using any weapon, only Magic!
4) I put no points in Mindreading or Wisdom.
Lockpicking: I put 1 point very early (in Farglow to open the chest nearby the Mage), and a second point when I was around level 10/12. Some levels later I killed Jagon and wearing his Necklage almost all the time now and that Amulet has a point + 1 to Lockpick ! (I'm now level 15). By the time (just before!) I go for my Battle Tower I give Jagon's Necklage away for having the reward solving the Quest killing Jagon (and other huntings

). But this is the way I DO. Just me.
Have Fun with the DKS !!