I'd go with the taller Velops, as they work well with our gigabit ethernet (via Cat6 cabling in the house directly connected to our provider, Windstream).
This is a mesh system, which means that there's a backhaul channel across all three routers essentially tying them together, and then each router has two wifi bands for depending on how new or old your equipment is. Having three such channels means there's no bandwidth sharing at all -- each device has full access to all available bandwidth (unless you specifically set something up in routing differently).
I don't think you'll have a problem covering 4k square feet, unless you have a bunch of walls all over the place, and if that's the case, you'll have wifi issues no matter how you set things up.
Yes -- the nodes just plug in. All setup is controlled via the mobile app, and after you answer a couple of setup questions, the system is pretty self-managing out of the box.