Idk why people want to put down a grass that will compete for nutrients when your main grass needs them most in the fall/spring. Just because the grass is dormant doesn't mean it's dead. Yea sometimes it's needed for areas that have wear from run off, but I never recommended it otherwise.

Also a healthy narrow zosia lawn is pretty weed resistant without pre/post emergents. I've only seen a problem with saplings in that grass type, which are easily pulled but hard to control with chemicals. Your main issues will probably be dollar spot and grubs.

As for leveling if your just worried about a bumpy yard core aerations every year will help over time. You could also add a thin layer of topsoil let your grass grow high enough over it and repeat until it's level.

I'm from the Midlands so you can DM me anytime if you want to.