I routinely use Seafoam in it to help clean any carbon. About every other tank I put a good slug in it. And yup I ride in the rain, not on purpose, occasionally. I know the water treatment too, I had an uncle with a 63 Pontiac 421 SD with 3 deuces on it when I was a kid, and he would pour a coke bottle of water through the carbs every once in a while to clean it out. It would sputter and blow carbon everywhere but it was a strong engine. I had an old Chevy Monza with a 350 LT1 in it that ran over 11-1 compression, and I had a vacuum switched water injection system on it to help with detonation.
You'll find that ridden normally, they get between 30 and 35 mpg. Of course you can make it do a lot worse than that without a lot of effort.
And what do you mean "used to wrench" on cars? Once a mechanic, always a mechanic. I'm 68 and I still don't trust garages.
The dual plugs on this fire at different times, and not always both of them. I don't recall the exact sequence, but at some rpm ranges it fires just one, and at other times it fires one and then the other/ And they do make Iridium plugs for the engine but I don't know about the dual electrode. On the M some folks like them and some don't, I run one heat range colder but not iridium.