I'm a fairly experienced welder & have patched stuff nearly as bad as that. But that was on cars that were worth the effort. That's not a job for someone with limited welding experience on cars, its a difficult enough job for someone with experience.
As others have said, go over the car with a screwdriver & check for more rust, there will almost certainly be more, especially where that hole is.
Used car prices are high & if that's a scarce model I would sell it on as a project & buy something else with mot. At worst you might get £200 for scrap.