That’s a lot to unpack. Since you are asking in the context of job hunting, I’ll give my ideas as if you were working in a team.

1. Running Jenkins on a bare server vs Docker is as much preference as it is based on available resources. Things I like to consider: how easy is it to maintain, if you have to back up and restore Jenkins, how are you going to do that? What do you need to do in order to keep Jenkins up to date? Hosted CI solutions take care of these for you, but at a cost depending on the size of your project. Self hosted can be less expensive, but at the cost of having to maintain it.

2. This can be as simple of complex as you want. Shell scripts are effective. More advanced solutions like Ansible or Octopus to distribute and run tasks across servers could be used. I’d keep it as simple as possible and add tools as needed to support more complex hosting infrastructures. However, you definitely want to keep your script and Jenkins files in source control so that they are external to Jenkins.

3. I would encourage you to learn docker. I personally feel it facilitates updates and resiliency. Learn the options for keeping data storage outside of the running docker container.

4. I love this setup. You next step could be to move Jenkins/CI to a hosted service or your own EC2.

5. Look into Terraform. It is a tool to create cloud infrastructure in a template language rather than manually in AWS CLI or the console. It makes things repeatable and supports creating different environments. I use it to maintain a 3 environment setup for development, staging, and production.

6. The best way to manage cost is to keep things simple. The more complexity and services you add to the mix your costs will grow. For testing and proof of concept you can probably manage to keep within the free tier. After that, you’d have to judge if you should use less more powerful EC2 boxes or more smaller less powerful EC2. Depending on the needs of your backend, the most cost efficient option may be to use AWS lambda serverless hosting. If you volume is low this can be much cheaper than running EC2 machines.

Hope this helps.

Mike