OK, I did only look on the general evenness, because you asked explicitly for Z-Offset. What you describe and what I seem to see in the image can have several reasons:
- Over/Under-Extrusion: I seem to see effects of both. So, first I’d do extruder calibration (there’s a post on that). After that, if you have some underextrusion, you need to play with retraction settings, mainly with “extra prime amount”.
- “Scratches” on the surface: I assume that’s what you mean by “not smooth”. To avoid the nozzle scratching across already finished parts, activate “Z-Hop”. Also, there’s “Ironing” that may improve surface quality if you want it smoother.
- Bad filament: Extrusion inconsistencies can result from low-quality filament - try a different brand if you’re not satisfied, but honestly, as far as I can judge from your picture, it does not look too bad after all…
Regarding too low/high: Your first layer seems to stick well in all places, so I guess you got that right. And again: Your result does not look too bad to me!