How big is the condo? My 2 floor house around 3000 sqft also still have good coverage using a single router. The least speed around 200Mbps. Unless you have metal wall

It is a semi-D and it is a build-up area not including land. It depends on the router you buy. Two floor is even more challenging because the floor is is concrete bar. The normal brick wall is easier to penetrate. Well, it depends on what you have inside the house.

I also bought Asus thinking that I could upgrade to mesh later because of Asus flexibility. However, it ended up that my speed test upstairs with door closed is still around 200Mbps even with 5GHz. The router was located near front wall besides TV.

Although Asus has a mesh set, you don't need to buy the set. Can select many model that support mesh and they do not have to be same model to my knowledge. Add mesh unit upon requirement.