OK, I´m new to Divinity OS Enhanced Edition modding, so bear with me plz.

Here´s a few things I´d like to do if possible;
1. Add some points to the level progression;
I´m thinking of raising the available attribute points from 15 to say 20, skills from 49 to say 55-60 and talents from 7 to maybe 10. Comments? Would that be OP?
Are there any tutorials available on how to do this or would I need dev rights to do so?
There are no 'dev rights', it can be done with Osiris.
The calls should be named something like
CharacterAddTalentPoints()
CharacterAddAttributePoints()
and
CharacterAddSkillPoints()
For exact names of the calls and parameters, you can type 'Character' in the story editor and it will bring up a suggest menu.
You need to use the game editor to use the story editor. The game editor is called something like 'The Divinity Engine Enhanced Edition' and on Steam it can be found in the 'Tools' section.
If you have never modded Original Sin, you surely need a tutorial to learn the story scripting language. There's a sticky somewhere in the forum to some video tutorials Larian posted on Youtube about story scripting. I believe that (almost?) every modder who does story scripting learned it from those videos.
2. Perhaps adding some basic loot to the game would be nice? Like adding crafting materials etc. to crates or corpses (a grisly job taking hair/teeth/bones from orc corpses etc. but hey, a source hunters gotta do what a source hunters gotta do right? :-D)
Also, there was at least one minable ore vein in one of Cyseals dungeons, it would be nice to have some trees etc. that you could chop down for logs which you could turn to different stuff for sale if you need the gold etc.?
That's really a lot of work, but it could be done. Of course there are no animations for chopping wood or for a cut tree falling, but at least it should be possible to create an object (a tree) that's usable and add some wood to the user's inventory if the tree is right-clicked ('used'), but as said, it would be a lot of work.
By adding more loot, the risk to stumble into the 'out-of-handles-crash' gets closer than in the vanilla version, so I'd recommend to be careful with that.
See Abraxas' explanation in the thread
How do you mod the EE? for the 'crash risk'.
3. As far as I know, the enemies like skeletons, wolves etc. don´t respawn, so once you´ve cleared the map so to say, there´s no way to "grind" more xp, so that places a cap on how far your characters can advance, right?
So, could something be modded, like a spawnpoint on the edge of map that would "seed" the map with new enemies (zombies, wild animals etc.) periodically?
Rhidian has proved in the Classic version that enemy respawn can be done through a combination of story and character scripts.
You could take his classic mod - think it's called 'Respawning Enemies' - and look at the code. Although it was made for Classic and not EE it should be possible to adapt the code for EE.
The question is if 'grinding more xp' makes sense without any further adjustment because with enemy respawn you'd overlevel the content even more as is the case already.
... and further adjustments are again *a lot* of work ;-)
There are my questions for now, thx for your assistance in advance!
Cheers!
Good luck and have fun with modding

You might want to take a look at the D:OS 2 forums even though the game is not released yet. But version 2 is supposed to make a lot of things in modding much easier than is the case in D:OS1.
Of course it's a different game with different story and different basic mechanics but I can tell you from personal experience that with the many bugs and deficiencies of the scripting APIs, modding can become quite frustrating in D:OS1, at least if you want to do more than simple and basic things.