The answer is it depends.
To put a full floor in you really need to remove the windshield, the dash,the steering column and of course the full interior except for the headliner (which you should probably protect by covering)
To put left and right panels in , you can manage without removing the windshield or the dash and steering column.
Also a full floor cut out will require bracing to keep things square while doing one side at a time and leaving the transmission tunnel intact minimizes the potential for twisting the chassis.
I would suggest that you consider the condition of the car. If the tunnel is nice and solid and the floors are just starting to rust through use the panels and preserve as much of the good original sheetmetal as possible. Just because you buy it doesn't mean you have to use all of it!
If you intend a rotisserie restoration to a Concours show car then (find a rust free car to start with) maybe a full floor makes sense.
This is all just my opinion- I'd PM Mister 4x4 he's replaced a pile of sheetmetal while building his car (I hear the only thing that is still original on his car is the vin tag and the right headlight trim ring)