My initial plan was to enjoy the game fully without mods at first and having then a second playthrough where I would use interesting looking mods. But during my first run I got so unhappy that you cannot retrain your companions properly, which lead me to the usage of mods.

I like to share/mention the three I can recommend right now, which can be used to address some issues with the game or give you a chance to experiment - as in: how would that class build look like up to level 20?

All mods can be found at Nexusmods at the moment

RespecMod by BarleyFlour - needs UnityModManager
This is the mod I started with, simply because I was so unhappy about the fact you cannot retrain your companions. When the mod was new I was astonished how easy and good to use it was. I noticed early on there are some things I did not dare to touch, like changing backgrounds and deity. Thankfully the latest versions have made those things optional and it feels quite safe to use.

However, like with all mods it is always recommended to make a proper backup and check properly if your changes did not break anything

Toy Box - needs UnityModManager
The probably most famous mod/tool which seems based on a tool already seen for Kingmaker. Using it for gold/exp and adding items to test seems very safe to me, and it has an additional option to enable achievements?
This one is which I use mainly to test level 20 builds. And for me as perfectionist it turned out very sour that mercenaries you hire do not have the same exp as your party.

Probably better to make a suggestion about the last thing... However, it is also useful to help you fixing quests when you missing or lost an item which cannot be acquired anymore.

Arcemi's Savegame Editor - comes with its own installer which seems safe (checked with RevoUninstaller + Kaspersky Security Suite)
This one I just used today since it addresses something which Toy Box did not so far: Crusade exp.
I might ditch this one very soonish. Right now it serves as a quick fix until the announced 1.0.5 patch gets released today, which is supposed to fix the Crusade exp system. Apparently there is currently an issue where you do not get any exp for defeating enemy armies. It was not like that on my first playthrough so I have to assume the issue has been brought in with a recent patch.

The savegame editor, is pretty simple to use too. In general you do not need it as you can edit the save game by yourself using an archiver app + any editor.

A guide for doing so can be found even in Owlcat official forums, posted by mods/devs there.

I can imagine how annoying it must be when you feel like you have to restart the game and redo many hours just because of a missing item or something else. So maybe these mods can be helpful for you as they were/are for me.

Make sure to do proper backups and cheat responsibly. You do not want to spoil your own fun by overusing it.

That actually sounds like a bug. I remember it was day one or two after launch, I found Radiance in the dungeon with the surprisingly easy to solve puzzle. Then I talked to Vane in front of Defender's Heart and he recognises the blade and promised a scabbard. When I met him again in Drezen I was uncertain if I missed the opportunity to get it. But he remembered!

It was such a sad ending for the meeting.

I second the savegame editor. Have used the other version for kingmaker before and this one seems to work just as well. Useful for those folks who don't want to crack open notepad themselves. Also doesn't require the mod manager, unlike toybox.