I want to be independent from hosts and their fees with raspberry pi for small projects.

What I’m trying to do

1. Create a spring boot app which would be accessible from domain
2. Make it work with https via Certbot and Let’s Encript
3. have a subdomain on it like console.mydomain.com or admin.mydomain.com

What I can do:

1. Buy static IP address from Internet provider
2. Buy domain and set it to point to the static IP
3. Buy Raspberry pi’s
4. Program Spring boot + Thymleaf + Vue ( Not that I can’t program in anything else, I have chosen this stack for small projects )
5. Have access to the router

What I don’t know:

1. After I bought the static IP, what do I have to do in the router, if any
2. If only I install certbot on Raspberry pi will it work and make my spring boot work with https? ( Along with spring configs… )
3. After I configured the router, in order to create subdomains for my projects or DNS server, what should I do ( By subdomain for DNS I mean e.g. dns.amazon.org but with my domain )

Thank you in advance for your patience

NOTE: Please do not send links which doesn't have full answer and if you do Please provide the rest in your answer

What I know:

I think I should setup a dedicated Raspberry pi for DNS server but for most of these kinds of projects I’m responsible for, there is only one Raspberry pi. So let me know if I can do all in one as well.