I apologise if you already know all this, but I hope some of it helps:
I used AustinBuddy's excellent YouTube video for learning how to properly set and balance my presets ).
After a while it just becomes second nature (for me anyway) to have the Vus up on the AX8 when writing presets with Axe-Edit and set the Amp block level to set the overall gain. Different people have slightly different settings, but for me I try to set my general preset level to around 0dB on the Ax8 Vu meter when playing hard, and up to +3dB for scenes/presets for solos and boosts.
As far as final level of the AX8 us concerned, which is global of course and set by the Output knobs on the AX8 facia, some people seem to have gotten hung up on AustinBuddy's comments that these need to be at 100% for unity gain. For me, I take no notice of this and set my final output level to between 70 and 80% because that gives me some room to easily turn up on stage if need be without having to go to my monitors.
Hope this helps
Thank you very much, this will be very valuable. Much appreciated.