All in order, no probs!
>SYS_PC
>Client_GOG
Had some Mods installed manually, so here's what I did before patching:
- Delete all folders in the Game's directory except "archive" (I also ignored "tools", which is for REDmod)
- Patch the Game* (was an approx. 6.4GB download for me, successfully patched)
- Verify/Repair Installation (was an approx. 143MB download, missing files from the earlier folder-deletion)
- Run the Game
*If you get the full 50/70GB+ Game re-download (which I did at first) try this:
- Abort the download (so your downloads tab is empty)
- Quit and restart GOG
- Initiate the Patch (from there, it was the mentioned 6GB download without problems for me)
To test, if everything was in order, I additionally did:
- Run Benchmark (no perceptible change in performance, with custom settings for 2.0)
- Play the Game/Load Save (as above, no negative change in performance)
From what could see, there were no problems with my Character, Inventory, Gear whatsoever.
But to be fair, I had not upgraded any Gear before the Patch yet, so the mentioned resetting of Tiers didn't affect me.
Also no problems from missing Mods, which is always nice

And the fixed car radio volume is great!
Hope this helps.
And cheers CD Projekt for your work!