Is there any community patch for The Witcher 3 like the ones for Dragon Age Origins or The Elder Scrolls series? I´m not talking about added content but about fixing remaining bugs. I´ve managed to find small fixes for individual issues but nothing like a real full size patch.

Do such patches also exist for The Witcher 1 and 2?

solved. it´s called "ghost mode"

That doesn't fix problems with quest bugs, it just rebalances combat and rewords descriptions, and other similar things. Sadly TW3 is still very buggy in terms of quest lines and there doesn't seem to be any mod to fix that. You might also be interested in the Nitpicker's Mod. A mod that some may prefer to the one you downloaded is FCR3, a combat rebalance mod that's made by one of the team members that worked on the TW1-3.