Have never used free dyndns services myself. But if I would have to choose one right now I would give ipv64.net a try. Dennis has some excellent (german) YT tutorials and constantly improves his services.

Yes, but if you buy there make sure to emphasize that you need the cage for the ssd. Otherwise you need to make an extra order over at harlander.com for 10€/cage, like I did. ;-) (But even then it's a good price). Yesterday I ordered a second NIC (Intel I225) for the M.2 slot. I hope it fits. Then I have 1 port for traffic and one for management. Cheers.

I now have three i5-7500t with each 16GB oft RAM and 256GB SSD and extra 1TB SSD for VMs and CTs, which are serving as a high availability cluster. Currently they provide my Nextcloud and Jellyfin instances but are overwhelmingly underchallenged. I'm planning to add all my docker containers to proxmox too but haven't found out what's the best way to achieve that.

I recently purchased three Lenovo m910q, which are now running as low-power proxmox cluster at my home for a very decent price. Here's the shop: http://www.manotebooks.de/ Quite happy with it.