Be extremely careful. Plenty of people are really smart and malicious, so you need to isolate it from everything on your network. You’re giving random people remote code execution on your local network, which is like the worst case scenario for security.
Zigbee, Z-wave, and Matter all should work, but they need special radios that require extra hardware on your server (except sometimes Matter—some devices use WiFi, while others use Thread, which is based on Zigbee). SkyConnect gives you Zigbee and Thread. Homekit usually works too, but at this point it’s better to get a WiFi Matter device. Anything running ESPHome will work automatically. Athom has a lot of products that are preflashed with ESPHome, so the firmware is designed by the same people that make Home Assistant.
.ovh domains are like $2/year, if that helps.