[mrlmd1]

By your own math, 3.4 gal tank - 0,8 gal reserve = 2.6 gal. If you get 60 mpg, that's a range of 150+ miles or so 'till you need the reserve, which might get you another 40+ miles. To be on the safe side, you reset the odometer every you fill up the tank and plan on getting gas at 125-150 miles and then you'll never need reserve and not have to worry about how far away is the next gas station.
I wouldn't worry so much about replacing or trying to repair inner tubes on the road. Are you going to carry spare tubes, patches, an air pump, tools to remove the wheel, break and reset the bead, etc.? You are not that far away from civilization and help if you need it.
If you peruse this forum you will find most of the answers to your questions. This is a very reliable bike in stock form and will last many, many miles/years with a little routine maintenance.,