Without a real examination (in person), i8t is hard to say if you need to remove the inner panel, but if you do, it is an easy project.
I cut pieces of my inner door panels off in order to properly hammer and dolly the welds on my (lower only) door skins.
If you are a fair welder and have a mig, it wont take a full day to weld the panel back in.
If it makes you more comfortable with your repair I say go for it. Just don't cut clean to the edge and there is no downside apart from the time you spend.
Oh, I just used a regular (1/16th ?) cutting wheel, it worked fine.
You might check EMS for a door panel.
<<edit EMS does not have door skins, sorry! They do make some other parts you might need though.)