The “1XP per combat phase” line should be ammended to “1XP per round” – it was always the intent that bombs count toward your damage dealt each turn, and if you score any kills with them, those count as usual.
Yes, enemy reinforcements are placed before players choose their dials that round, unless otherwise explicitly stated in the mission special rules. The Elite TIE Phantom in “Bait” is an exception if I remember correctly.
I suppose you could do it the other way, but it’s likely to either have zero impact because enemies spawn far away, or be extremely frustrating because enemies spawn right on top of you and you don’t get to react properly. This inconsistency makes it a poor choice for a difficulty tweak.