It definitely sounds like you have some challenges ahead. I personally prefer MoCA over wireless, simply because you can control what devices are able to be a part of the network, and reduce the overall interference from external sources and connections.

With WiFi, being half duplex, only one station can transmit at a time (with come caveats). Whether that station is a part of your network, or it is simply operating on the same frequency/channel, doesn't matter. So in high density environments, you can kind of get screwed by neighbors.

MoCA is also half duplex (at least it was the last time I checked) so having a 2.5G MoCA link, to a 1GbE connection (on the ethernet side) should provide similar, or the same experience as pure ethernet (1G full duplex)... The "extra" bandwidth on the MoCA will allow for each station to send and receive at approximately 1Gbps without stepping on eachother so much that you have degraded performance.

However, it really depends on your situation to say what should or shouldn't be setup. I don't know your bandwidth requirements, so I can't really say. The nice thing about ethernet is that it on switched networks (which is what you'll be using for gigabit), the. Ethernet kind of naturally defaults to the shortest path, unless you're doing something foolish with it (like intentionally messing with STP to push traffic in a particular direction). The issue with that is that ethernet doesn't really scale beyond a few thousand nodes. Not an issue for even a fairly large LAN, but that's the reason we don't use it for internet (wan side) traffic routing. But now I'm off topic.

Given the naturally shortest-path behavior of ethernet, of you have a switch in your office and you only really use your NAS from your office PC, you'll have a full speed experience. If nothing else needs high-speed access to the NAS, you'll be fine.

Apart from the NAS or any other LAN resources, the network should be sufficient to fully saturate your internet connection. So the average WiFi speeds should be targeted towards something faster than your internet link (again, half duplex factors in here). I don't know your internet speed so I'm not going to even guess what the numbers should be, but I personally aim for double my internet speed for maximum throughput on my WiFi as much as I can. The closer you can get to doubling your internet speed here, the better. Anything more than that will likely be wasted.

There's a ton to say about WiFi and performance optimization, but I'll leave it alone unless you ask about it further.

Good luck.