Switch and Router Connected Directly to ONT

Hey everyone,

I have had an idea brewing for a bit now on how to fix the Wi-Fi upstairs. Long story short, we have a pretty big house that's been finished already. The previous owners only wired the first floor for Ethernet, and I've already ran a 100ft cable downstairs to the basement from the router to hard wire there. That leaves the upstairs above the garage basically a dead-zone for wireless. I'm talking speeds of around 1mbps when we have internet 750.

So anyways, my idea was to connect port one of the ONT to a dumb switch that I have already, which then connects to a Nightgear R7000 setup in AP mode via the LAN port. I would still be using the T3200M and the Optik TV boxes as well. So basically it would go like this:

ONT -> Switch -> R7000 in AP -> T3200M -> DLink in AP

Quite a bit confusing, but please do let me know if you notice any glaring issues right off the bat. I've tried it once and made it work properly, we get speeds of 400Mbps upstairs now with pings of less than 5ms but I want to make sure I'm not exposing any security flaws or something along those lines to the outside.

Thanks for your time everyone!