Yes just remove the vent clean the roof pretty well. The AC’s come with a foam gasket that needs to be crushed to make a rain tight seal. You want to clean the old sealent off the roof (be careful what you use, petroleum products will ruin your TPO roof). Then seal the old holes from the screws from the vent, I would use self leveling, small amount in the holes to fill them so you won’t have a leak. Let this dry for hour or so before installing the AC.
Yes the run them to the light switch area in the master bedroom. You will have to cut a hole and mount the thermostat you want to use.
You can mix brands and sizes.
I suggest put it in the bed of the pickup. Backup to your trailer as close as you can on the side. Then get two or three folks and lift it to the side of the truck. Then you can get a good grip under it and have them place it on the roof.
If you know someone that does roofing they may have a ladder with a lift or beg someone with a forklift or front loader to help you out.
Here is two part video on someone doing the install in a Reflection.
Part 1 install:
Part 2: wiring: