[MANGA SPOILERS] Some plot holes I can't fill

So the manga does a pretty good job of filling in plot holes later on, but there are still a few things that don't make sense to me.

1. Why did BRA wait 5 years to attack Wall Rose? Maybe I'm wrong, but I thought their objective at that point was to wipe out the Eldians to get resources for Marley. They didn't know about Eren at that point so why wait and why join the military at all?

2. Why did Zeke seem like he never saw 3DMG before the first time we see him as the Beast Titan? Does that mean he has had zero communication with BRA since they attacked the wall 5 years ago and that he never saw an Eldian in the wall before then? Why didn't he infiltrate the wall with them? And for that matter, why didn't the quad titan infiltrate too?

The best explanation I can come up with for any of this is "because plot". I'm hoping some of you have better explanations.