I enjoyed wizardry 7 and didn't find it to be too difficult, so my question is, how hard is wizardry 8 in comparison?

8 is easier for sure. And not as long as 7

I also enjoyed Wiz7 back then and have just started a game in Wiz8. Now I have less time and the length and difficulty (its UI and usability required an effort in the player side) in Wiz7 would be a concern for me today. Wiz8 hits some sweetspot in this regard. It's like playing a friendlier Wiz7, I bet you will love it as I already do.

Actually, in Wiz8 it seems more necessary to keep your back against a wall. Otherwise monsters keep surrounding your party all the time. And you easily get pretty big mobs attacking you. I don't recall this was so decisive in Wiz7.

Wiz 8 is a true 3D game, unlike any of the earlier games, and you see the enemies (where as in 1-7 they just pop up; not sure about 3, but M&M 4-5 had the ability to see your enemies a couple of steps or so before encountering them). But yeah, keeping your back to a wall (or better, a corner) is a very good strategy in 8.

But in terms of increasing difficulty, setting it to Expert and Iron Man would make it so.