GPS tech (Garmin, Hammerhead, Wahoo, RWGPS, etc)

Can you save .gpx to your phone, and then upload to wahoo? via bluetooth, no network.

No

Do you have a wahoo app, that you upload from, does that import .gpx or do you make the .gpx in the wahoo app.

You can do either, import a gpx or make a route in the app

Can I upload from ridewithgps?

It syncs automatically with RWGPS (if you have network)

I very rarley re route on the fly, and if so, I normally use google maps to do so. As someone point out, so wahoo maps would properly be fine.

In my experience it all works well unless there is no data connection and then it can't do anything apart from what is already on the unit.