I already have Morrowind and Oblivion and Two Worlds 1+2, what else shall I get?

What's the point? Your account is going to be deleted soon™

Schizophrenia is a thing. Present you the evidence...

Common sense.

None of these are currently on sale if thats what you mean by cheap but keep an eye on them & grab them when they are:

https://www.gog.com/game/vampire_the_masquerade_bloodlines
https://www.gog.com/game/fallout
https://www.gog.com/game/fallout_2
https://www.gog.com/game/arcanum_of_steamworks_and_magick_obscura
https://www.gog.com/game/fallout_new_vegas_ultimate_edition

I personally also liked this one:
https://www.gog.com/game/fallout_3_game_of_the_year_edition

But FO hardcore fans would not quite entirely agree here :P.

Like Oblivion/Morrowind the modding depth for both FO3 & NV is massive.

Divine Divinity will keep you busy for 100 hours for usually .97usd

Hard to get any cheaper than free at that point. It goes on sale a lot. So wait for it.

Elex
Elex 2
Greedfall
Risen
Risen 2
Risen 3
Gothic
Gothic 2
Vampyr
Vampire the Masquerade: Bloodlines
Fallout
Fallout 2
Fallout New Vegas
Baldur's Gate
Baldur's Gate 2
Icewind Dale
Icewind Dale 2
Neverwinter Nights 2
Star Wars: Knights of the Old Republic
Star Wars: Knights of the Old Republic 2
Jade Empire
Grim Dawn
Titan Quest Anniversary Edition
Diablo
Hellpoint
The Surge
The Surge 2
Horizon Zero Dawn
The Witcher
The Witcher 2
The Witcher 3
Cyberpunk 2077
The Outer Worlds
Arcanum: Of Steamworks and Magic Obscura
Silver


Not on GOG

Dark Souls: Remastered
Dark Souls 2: Scholar of the First Sin
Dark Souls 3
Elden Ring
Star Wars: Jedi- Fallen Order
The Elder Scrolls V: Skyrim
Grandia II


This should get you started.

What starting character and base tactics would you recommend for that one? I tried a she-warrior with the spinning movement, for some reason ended up using a bow a lot. Not too happy about that decision, it was hard to fight the vampire, orcs...

I haven't finished it but I recommend Divine Divinity. I've often seen it described as an isometric Morrowind with Diablo-style combat and that's a pretty accurate statement. Even at full price, it's only $6. According to HowLongtoBeat, a leisure pace (which is ideal for RPGs) takes anywhere from 43 hours to 90 hours for a completionist playthrough.

Also, you can't really beat the classic Fallout games. They're significantly different from the modern games but they're still 100% worth playing if you enjoy story-heavy RPGs with lots of choice and consequence.

Usually play an archer mage. I find the distant a lot more palatable and as long as i can kite the enemies, I can make it through most areas with fewer upgrades.

(Fully back the recommendation if you want to see an ARPG done right. But the games mentioned by the OP don't seem to go at all in this direction.)

I played a mage (as always), and doubt I did much with bows. Relied on them in Divinity 2, but in DD, really don't think so, magic gets good enough fast enough, if you're quick on your feet. But it is an example of early pain for later gain, because just about any spell can be learned from books, which can be found (if I recall correctly, there are four Restoration books in the game - and there's a small chance of a skill book in bookcases) or bought in stores. They're expensive, so you'll be struggling with very basics at first, but once you get enough money, save before checking a store that may have books after the inventory resets and keep trying until you find something useful (or get bored, sometimes it'll just take too many tries, of course). That will free up the skill points for other skills.