Is there some mods for hd or something else I should be aware of?

There have been some fan patches in the past for higher resolutions, but I believe the massive 1.1 patch that GOG automatically offers far surpasses all of these, as it offers support for high resolutions and much more. There are no other necessary mods or patches that I am aware of :)

As Syrion said, Outcast 1.1 should be fine without any mods. There were a lot of patches to it after release but those seem to have slowed down, and the current version on GOG should be the latest.