For something like that, you’d want a VPS with 2-4 cores, 4 GB RAM, 80 GB SSD. Any less and you’ll start to run into problems when adding bridges and stuff.
So, it’s really a matter of what deals you can find in that bracket, and if you care about the geographical region it’s hosted in. Usually https://lowendtalk.com/ is a good place to start looking at options.
I think what you have is fine, and wouldn’t worry about it too much.
That said, I run unbound with pi-hole, directing the dns queries through a wireguard tunnel. It’s a bit slower, but I do like having my own recursive DNS, especially with news that more and more services are implementing DNS level blocking.
You can also just copy your thunderbird profile directory, if it’s the same OS, to a different system and it seems to just work. I did this to copy the whole setup and synced mails from desktop to laptop. I also tried this from Windows -> Linux and it did not like that, so I used the import profile feature and re-entered all the passwords.
I’ve used Ansible to deploy docker compose and it worked pretty well. You will have to do some learning if you aren’t familiar with it, but I’d say it’s worth it.
Like others, I would not recommend Jenkins.
I happened across this tool to help you create configs, it looks pretty good, easier than piecing together all the parameters separately: https://www.digitalocean.com/community/tools/nginx
Seems like it has directions for certbot and generating dhparams, etc. as well.