recently bought 2 of the beelink mini PCs - they seem pretty solid so far - they are quite a bit more expensive than the pi but I think they offer pretty good bang for the buck for a small form factor server.

is your router’s dns definitely pointed to the pihole and was the router rebooted after that was set?

Connect the router’s WAN port into the cable modem. Plug your stuff into the router LAN ports or connect to the new router wifi. Set pi hole to a static address and then set the router’s DNS to point to that. Remove any secondary DNS in the router settings. Reboot everything and make sure it all works. That should be about it.

For any well-known software, ChatGPT – although it pains me to admit it it – is surprisingly good at providing reasonably clear installation and setup instructions.

Go for it. the specs on the laptop are good enough to run plenty of stuff as a server. As long as the drive can be mounted you should be good. Your backups should be somewhere else.