Every target gets hit by a separate attack.
If one of those attacks is a crit, that target takes critical damage and effects.
If one of those attacks is a hit, that target takes hit damage and effects.
If one of those attacks is a miss, that target takes miss damage and effects.
Do you max for that one and just roll the damage for the others who are also effected?
You only roll for damage once per attack
Strangely, with bursts and blasts, I find it easier to roll the damage first, then roll the attack rolls. So, say, you get 10 damage, then you start pointing at minis/declaring targets and saying 'hit, 10', 'hit, 10', 'crit 25' and so on so forth, rather than having to remember what attack roll you got on whom if you do all the attack rolls then the damage.
I do exactly that.
Agreed. When resolving area attacks, it's so much easier when players announce damage, then start announcing who is hit or missed.
The hard part is getting them to remember to do so.
YMMV. I prefer my players to figure out who was hit and who was missed, and then we process whatever damage rolls are required ("You pre-rolled all the damage including crits? Pity you only hit minions.").
In either case, the important thing is not to stop the sequence attack rolls for damage rolls. Roll damage either first or last; don't stop in the middle.
Strangely, with bursts and blasts, I find it easier to roll the damage first, then roll the attack rolls.