Well it won't. You either tell it to assume that say oldest is always source and if there are identical files then you get asked to choose.
Depends what you set in the DNS records and where you published them? Literally no idea tbh.
You can't possibly know that from the limited info in the OP.
Zerotier, or any other VPN service that is outbound/cloud hosted.
All I can say is, wut?
What bottlenecks are you experiencing on which services exactly?
If DNS is a burden to support you're doing it wrong. I set it up once and haven't touched it since. Everything new that gets added "just works".
Gmail, and add your domain as an alias?
I've looked at a couple of these type things (including Portainer and CosmosOS) and they just add another level of complexity. https://github.com/louislam/dockge looks to be a lot simpler and allows you to use commands that everyone is familiar with.
Whilst I have pretty much everything backed up where I can the only things that I have actually got 100% tried and tested recoverable is Hyper Backup (as it encrypts my B2 backup) and within that is my Vaultwarden backup. So even if my lab was destroyed tomorrow I could get to my B2 backup and recover the Vaultwarden backup and stand it up on any machine I could get access to.
I am not very good at the local backup thing but I do also have an unencrypted backup that is run less regularly that I could easily grab the Vaultwarden files from.
In addition to that the vault is accessible locally if it can't communicate with the server anyway.
I'm going to assume everyone here saying use docker is fully conversant with docker already. As someone who already happily has multiple services hosted on multiple (extremely light) VMs I would say just leave docker alone. I have spend most of today trying to get some containers in docker working (reliably, which is what a lot of people miss). Yes getting docker up and running and containers working is simple, but if it all goes sideways tomorrow what are you going to do? What's your backup plan? IME it's much harder to get a docker stack back up and running using your own data than simply restoring a backup to a VM host. There are a couple of things I want to use that are docker only and there is something to trip you up at every turn. It's another level of complexity you don't need. If you have a working environment now then why would you need to add docker?
The only thing I would say would be to maybe use a different distro for hosting everything on, but overall "if it ain't broke don't fix it".
The correct answer has been given a few times here, split tunnelling.
But your idea is mental. If your IP changes and access is locked down by IP address how do you expect your phone to connect to your server to tell it about the new IP if it can;t access the server due to the fact it hasn't got the correct IP in the allow list?