All seven wheels should be the same and mount in any/every wheel position.
We just crawled through this with another member, it seemed the decision was going to be to stay with 16.5 tires.
Read
This Page and be sure you understand OFFSET. Offset produces the required spacing between dual rear tire sidewalls but it isn't measured that way.
How do you plan to use this coach? Like how far do you want to drive? Stay away from your base how much/how long?
The Firestone Transforce is a good tire and the price is reasonable.