Congratulations, I also bought a Z8 a few weeks ago after a break from photography for a few years, but circumstances have changed and now I can spend a lot of time with a camera again.
Switching to Nikon (from a Canon 1DX/7D) and mirrorless takes some learning but I love the camera and the lenses (14-24, 24-120, 100-400, 105 micro and the 600 and 800PF + 1.4x). The 800PF was one of the main reasons I chose Nikon, the 600PF and the Z8 other convincing reasons, but also the other lenses. The 800 is really light for such a lens and here in southern Germany everything is shy (except some birds in parks) so 600 is mostly too short anyway. The 600Pf will be great for hiking and traveling, though.
I bought Steve's books for the Nikon AF system, his wonderful BiF book and the Z8/Z9 setup guide. They are very helpful.
I also bought Thom Hogan's Z8 guide which provides loads for additional info over the manual and I also got a lot from the Steve's Youtube Channel and the channel of Jan Wegener, who also has great videos for how to set up the Z8. Highly recommended.
Mastering the camera will take time but for me that's a fun process.
Have fun with your Z8, I am definitely having fun with mine.