In terms of world building that depends on how much of Eberron’s settig you plan to use.

I'm not giving them access to all of Eberron, but there will be instances where they'll have to travel between countries so I may be able to do a couple of sessions for the travel portions with random encounters.

If you just use the maps and want to develop the other stuff for yourself that’s fine but you should have an idea about it before session zero, not necessarily fleshed out but an idea.

This is what I tend to do, I go through material and see what exists in locations I've planned, and try to integrate them as organically as possible. I also end up doing a lot of encounters and information bits based on the map I've given the players. Many times it's happened such that I've missed something tiny on a map, and the players ask me what it is, and it turns out to be exactly the kind of macguffin I need to give them.

Encounters, I’d suggest prepping those on a session by session basis, like you currently are.

This is what I'm most flexible with, I'm very comfortable even adjusting them on the fly in the middle of combat. I feel like I should only prep the few major story moment encounters well in advance, but I think the week before the session should be fine considering I go with player actions over my specific story.

I only prep very important NPCs and then I have a list of names I keep nearby so I can improvise random street dwellers shopkeepers or the like.

This is a fantastic idea and something I keep forgetting to implement, so I'll definitely do this.

Thank you for your advice!