You can do this anyway that you like. If you do the wall first you'll need start above the first row (ie Ledger Board) so that you can lay the floor in and then cover it with the wall tile. You'll need at least a 1/16" gap between the wall tile and the floor tile. Before you grout you're going to fill the gap with 100% Silicon Caulk. You'll need to tape off you seams to accomplish this. Also you'll want to make sure that your first row on the wall is a cut. Due to lack of levelness your full tile maybe unable to cover the gap, the floor may be off relative to the floor.
If I were doing the job I would likely do the floor then I would lay the first row and using a laser level I would level out the first row and let is set over night. The next day I would take it up to the 5' mark. This would save me having to set up a ledger board and cut the first row. I would just throw a tarp down to protect the floor from the thinset or grout.
Does all that make sense?