The only areas I had not explored were the stronghold of the Black Ring necromancers and the canyon.

The Black Ring soldiers in the quarry may be a little tough when you first get there, but even another level or two could take care of that (the tower is locked until later). In the fjords there is no direct harm if you fall off the mountain path, though that could mean having to get past a few opponents making your way back up again. If you are careful, though, entering the fjords early isn't particularly dangerous (still a risk for a once in a lifetime challenge), especially for a ranger.

it was a bit annoying there were no stat points left for Intelligence, Dexterity, etc., and as I took damage so quickly even with this build, it would have been impossible to ensure survival if I had raised other stats as well.

Actually, I think raising other stats would have helped. Strength improves your melee resistance and healing rate, etc. After the start of the game I got most of my hit points from equipment bonuses (Life Line was almost always my first choice for armour enchantments). In DKS, playing a ranger on nightmare, I finished the game on level 47 with 1216 hitpoints (306 without equipment) and 54 Vitality (14 without equipment; I stopped distributing stat points after level 15).

No level-scaling, please!

Of course not.

Imagine running into a lone death knight 10 levels higher than you and carefully sidestepping his crossbow bolts while you fire your own at him, sometimes taking a lot of damage but spending many health potions to keep on fighting. Finally he drops dead! You get a load of experience, his sword and his shield, or just a random drop of items 10 levels higher than you. Now imagine that you couldn't use his sword because of its high level!

Well, that is something to look forward to, then.
My first game in Divine Divinity I took out the knight you can meet by Stormfist castle and got a very nice two handed sword for my efforts. I had to go up a level and use a gold strength charm (lucky drop from the dragon rider Zandalor kills) to be able to equip it.

Or imagine that you don't get full xp, because that would be "too good" and give you a couple of full levels from just one monster.

On level 1 in Divine Divinity you could get to level 3 killing zombie Jake (with a lot of hit an run with a bow, or a moderate amount with Meteorstrike) the first time, and then level 4 the second time. In Divinity 2 the experience bonus was limited to 50% of what an opponent would give if you were at the same level.

If this game is like others in the Divinity series and monsters don't respawn, you actually lower the amount of xp you will get during the game if you take on monsters of higher level than you!

Actually, the extra experience from defeating higher level opponents makes up for the less experience for lower level opponents, and if you do everything you end up pretty much at the same level regardless of what order you did things.

Those of you who have bought the alfa/beta tester Kickstarter offers, would you be willing to test the fairness of the "very easy mode"?

A couple people have done perma-death challenges with DD (A Survivor must become the Divine without dying) and Divinity 2.

Do you feel it is worth to balance one of the game's difficulty settings only for an experience players can have one single time, a challenge most players won't even try out?

Probably not specifically, but much of what you suggest is worth considering for the difficulty settings, anyway. There may be some design details that are unlikely to be changed at this point, but they are still tinkering with Dragon Commander while getting it ready for release, so you never know.

Is it possible to resurrect without being close to the body, then?

That is unknown. Resurrection wasn't implemented yet in the game builds shown in the kickstarter videos, and the cost had not been determined.
If one character gets into an impossible fight and dies, it wouldn't necessarily be a great idea to force the other character to face that same fight to be able to resurrect. Too high a cost would also just have people saving before fights and reloading if anyone dies, which is not very immersive.

you can have the computer controlling one of the heroes

You can set the personality type of a character so the game will select appropriate conversation options, but in sinle player combat you control all the characters in your party.