Openwrt generally works great on x64 PCs. Thiss machine will most likely be more beefy than your home router and could become your main firewall. It can handle adblocking and vpn client for all PCs on the network as well or whatever your need, as openwrt can do many nice things no commercial router can do out of the box. Install openwrt on your home router as well and use that as access point (connected via cable). You will improve your wifi signal as well. If your machine does not come with rj45 lan ports, install usb3 to rj45 adapters to the usb3.0 ports. They will give you the full 1000 mbit speeds.

You need to change the nginx config (for the website you will be hosting your services at. /etc/nginx/sites-available/yourdomain.com

You can reroute all http requests to https in that config.

Watch a video on how nginx works and how to set it up, and then look for example nginx configs for your services. It’s a pretty standard setting nowadays so the syntax should be easy to find.

I think nginx can be setup to work locally only, but do you even need it for that? It’s primary use is to proxy http requests to the different websites running on your server, enable https via letsencryt and so on, I think.