Setting up Zigbee network on 4 floors: ZHA or HA supported Zigbee GW?

Another similar product is ZigStar LAN Gateway

https://zig-star.com/projects/zigbee-gw-lan/

https://community.home-assistant.io/t/zigstar-zigbee-coordinators-and-routers/338586

https://www.tindie.com/stores/zigstar/?ref=offsite_badges&utm_source=sellers_mercenaruss&utm_medium=badges&utm_campaign=badge_small

No such known issues with latest firmware, but yes you will need to upgrade the firmware regardless.

Yes you can but it has a Silicon Labs chip so not recommended if ever want to try Zigbee2MQTT later. Function-wise it would once hacked work similar to Tube’s Gateways and ZigStar LAN Gateway.

Still, I would not recommend something that requires hacking for first time setup when a USB is very cheap and can be re-purposed as a Zigbee Router with different firmware if want to upgrade later.