Since 1-3 are answered, I'll throw in my thoughts on 4. I had two #5 tanks. When I moved, the new supplier charges $2 (that's TWO bucks) more for a #10 swap, compared to a #5. Tank upgrades were only around $20, so after the second refill, I'm ahead.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk