Welcome.
We left Fl. 5 years ago after being feed up with smoke and mirrors for 17 years. It is really like a magic show. All an illusion.
You bucket list sounds great.
The E350 is a Standard Ford build. They are built to work on the gas of today.
I have a 2000 E450 with the V10 and have run into NO problems with gas from any station. The engine management computer does a good job. I use no additives.
If however you want more power, the same computer needs to be re-programed. I have not yet made that change, however from my research 5-Star Tuning is the way to go for a Ford. It changes the engine operation parameters as well as shift points. We all know that the factory settings are a compromise, to meet the many different environments and regulations.
The Ford E350 and E450 are Commercial workhorses and are well proven for reliability.
I hope you enjoy the Journey.