Hey, I also played Cross before Trigger! Totally changes the perspective, I think
1) The Dream Devourer is meant to be an intermediate step in the evolution to the Time Devourer, aptly named because it feeds on dreams instead of, well, time.
2) CT:DS seems to have retconned Guile being his own character, so yes, he is Magus (with amnesia).
3) If I remember correctly, after fighting Queen Zeal the Black Omen becomes a portal to Lavos, where the real fight then begins. Though I could be wrong on this.
4) It is suggested, but not stated. There are reasons for and against both arguments. Dalton is the reason behind Porre's sudden rise to power in Chrono Cross.
Yeah, some of it does seemed forced. Probably because, just as Cross tried to add throwbacks to Trigger, CT:DS tried to add throwbacks to Cross. It does tie the two games together more. However, simply telling us so-and-so happened is bad story telling.