Really good guide OP, thanks for putting in the work.
A note on 'Spreading the Love' (Hit 5 characters with an area attack). I got this in the campaign as soon as I threw a grenade that caught a group of five enemies within its blast radius - they did not need actually to be caught by the blast itself (which in fact most of them weren't).
this obviously makes the achievement far, far easier to get!
The mission at the end of Act I, where you have to defend a gang boss against another group of gangsters, worked well for this. The second wave of gangsters spawned in a tight group near a car, and so were perfect to catch in a single grenade's blast radius.