Good Day Shay,
The standard welder qualification test is different from some things you will run into in production.
Once the standard test is taken the welder is qualified to weld 1/8" to 3/4". The 1" test will qualify them for unlimited thickness.
But, looking at the preapproved joints in Clause 3 Figures, you will notice that open root, single bevel, with no backing is not a preapproved joint. This is because of the stats that were used when setting up the program. In an effort to assure the highest probability of success in welding, certain materials, joints, processes, and other restrictions were arrived at that have been used and proven successful for a long time.
Now, per your query, not using backing is not an issue if there is backgouging involved. But, if you are only welding from one side you need to perform a PQR to prove your process and technique will work. Then, the welders would have to be tested to the WPS developed from the successful PQR. But, your welders still need to be tested and qualified per the standard test from Clause 4 (Clause 6 in the 2020) of D1.1.
Now, following that train of thought, if you use the standard test, and the welders are welding from one side of a joint, but backgouging is used to finish the weld, they are good to go. Everything else only applies when no backgouging and welding is done from the second side.
The answer to your final questions cannot just be a judgement call that we make for you. You must decide exactly what is needed and how the production welds are to be done. Giving us more information will help us to give you any more guidance that may help you to go the direction you need to go.
Have a Great Day, Brent