All of the above!
Cost difference between a 250/2500 truck and a 350/3500 single rear wheel is not that much. Go with a SRW 1t.
For FT living, you're going to want something more well-built, NOT any "light" model, which means weight. Go with a SRW 1t.
Short term, there was a guy on RVTrader selling a Jayco Eagle HT 27.5RLTS and RAM together for about $55k. Combo packages are out there, if you're willing to take used. This Jayco would likely work for a few years if you don't winter in extreme temps. You could then upgrade the FW to something nicer. The truck would likely last a lot longer than the FW.
Lyle