I wanted to play the Witcher 3 again, so I figured I would play the first two games and read the books at the same time (given in the first two games Geralt has amnesia from what I've heard) and quite frankly this game is hard to play. Not very involving or fun combat.
Any mod I can use that doesnt just improve it, but completely overhauls it?

I haven't tried it, but a mod often recommended by those who didn't like the original combat system in The Witcher EE is Full Combat Rebalance.

The combat system of TW1 is unusual, but you will get used to it soon if you practise it for some time.

Lclick when indicated:

https://www.youtube.com/watch?v=-azUnJGx-Ok

A click in TW1 doesn't mean a single hit, but a combo of two or - later on - several hits. Don't interrupt the combos.

Geralt is a talent for motion. If you want to avoid damage then Geralt should dodge. You can manage that by double clicking the movement keys W,A,S or D. By double klicking "W" he jumps over the heads of his enemies, and after pressing "F" afterwards, he will turn around immediately:

https://www.youtube.com/watch?v=wC-lOJ8LWcQ

Important: Choose the proper style. For small, quick monsters and humans with bad armor "Fast Style". If you choose the wrong style this will happen:

https://www.youtube.com/watch?v=9xSl7G2xtIo

So you have to change the style:

https://www.youtube.com/watch?v=hckP95OqwJY

For details read Geralt's journal (Ingame: Press "J" -> Tutorial).

If you combine the basics with signs, oils etc. then you will see that TW1 combat is fun:

https://www.youtube.com/watch?v=_naT3fQB0KU

https://www.youtube.com/watch?v=tVZsTEjmWvk

https://www.youtube.com/watch?v=mr9x0XmfsTA

A lot of fun for the player - instead of frustration.