Personally I’m waiting for Ghost to support Activitypub but generally exposing WordPress is perfectly fine.

Use whatever you have and test different setups. I would start by installing Proxmox and setup ZFS on some drive that not the boot partition. For just checking it out with some lightweight VMs and containers any CPU that’s not 20 years old will suffice, the more RAM the better. Play with VMs, backups etc in small scale. You can use your old external USB HDD, etc, just to figure out things like ZFS.

Don’t buy anything before getting some experience and having some kind of plan.

Hm, I never really liked Conversations and decided to end xmpp for good. Maybe I need to give it another try but I really like some Matrix features.

Better mobile clients? Have things changed this much in the least three years?