Not quite as you say. Top seed isn’t guaranteed to always meet the lowest ranked seed left, like in the NFL. It’s more like tennis or darts, where the path is predetermined and you can plot ahead who you are most likely to meet in upcoming rounds. Like those other sports, the table is in two separate halves. So from as soon as the last 32 is known, you will know for a fact that you can’t meet 16 of them until the final.
And yes, for your second point. The knockabout path is 100% determined on where you finish in the group. So previous opponents and same counties is irrelevant.
Although not sure if they’ve got some plan for when countries at war, or who don’t get on very well, might be due to meet?
The only restrictions are on the group opponents. They say they will try and keep teams from the same country away from each other. But for countries with five, or theoretically even six, teams, they can’t guarantee it.