To make PCs of the sort that are viable and be what the player wants to play, I allowed them (or optionally me) to roll 4d6 and use the three higheest dice. totals could then be arranged, as I added bonuses for Str, Int, Wis, and Dex, not just Str and Dex.
Do you use the weights on M&M p.15 for encumberance, or just wing it?
My group is veteran, and they don't overload, so that's not a consideration. I pull out those rules only if someone is abusing the amount of equipment they claim to be carrying around.
Do you ever use reaction rolls? (I've always found them to be one of the most seldom used mechanics.)
Not often, as almost everything in the dungeon is hostile. Reaction is thus a foregone
Cheers,
Gary