I think your GPUs are going to prevent you from using the 10.14.0 USB installer. Your item #1 is correct ("Not being able to run USB installer because of GTX 680 bug"), but you probably can't use your 1060 either because it requires Web Drivers to be recognized as a Metal-capable card, and those won't be installed from within the installer. So the install will not proceed saying that you must install a Metal-capable card to continue.
If you have the time, I really think it would be worth it to try using dosdude1's patcher to make a new USB installer. I tried this last night and was able to install to an encrypted drive, whereas the stock USB installer prevented that. Dosdude1 is a trusted contributed here, and he's been doing this for a long time. So the risk of something going wrong is really quite low.
In fact, you'd also be helping the community here, because I'm not sure if anyone has tested whether or not the mods he made to the installer disable the check for a metal-capable card or not. If using his modified installer allows you to proceed with the install (either with your 680 or your 1060) then it could be a solution to others here with NVIDIA cards who prefer to do a clean install via USB.
It really doesn't take long to make the installer drive (especially if you already have "Install macOS Mojave.app" downloaded. Just download the patcher
here and follow the directions. You will get a message that the patcher isn't intended for your model (since it's designed to be used with Macs that Apple dropped from the compatibility list) but it will happily proceed past that to make the USB installer.
If you decide to try it, please report back your results!