Just hitting a couple of these:
"Do Johnson's get together and have conventions? Like with seminars and to swap stories?"
Sticking with the "Three basic types" in MJLBB, I would say Corporate Johnsons likely do have conventions and seminars of a sort, but it's handled in much the same was as all their other business, secretly. Marketing conventions with backroom seminars about teams in a specific areas and local customs in different cities, that sort of thing. The other two, it's highly unlikely, outside of "three Js are in the same bar and get a conversations going."
"Do shadowrunners and other people named Johnson get mad at Mr. Johnsons for using their names?"
I would think it's like people who are named "James Bond" or "Jason Bourne" right now. They find it amusing, especialy since "Mr. Johnson" would definately be known to the public via media representations. They're are likely even some "strange' people with the last name "Johnson" who named their kid "Mister" to be "original and hip."
"What was the first spell cast by a metahuman? I think something with fire personally, I'm always trying to burn people with my mind."
I'd bet Shamanic, and I'd put my money on something that would eventually be really dangerous but because of their untrained nature, was merely frightening and cool ]if the user noticed thay were the cause at all. For instance, powerbolting the car that just cut you off while flipping you the bird or manabolting that annoying old woman at the stuffer shack, the one who comes in at rush hour and is paying in pennies.
