Don't worry, they serve very different purposes. You already probably know but Docker is for running applications in isolation, while Ansible is for provisioning and configuring hosts. For instance, you won't use Docker to harden sshd on your hosts but Ansible.
You may want to put some effort (not that much) into managing your credentials with Ansible Vault[0] and you can try your playbooks e.g. on a Vagrant Machine[1] before applying them to a real host.
Any tutorial will do for the beginning but you should always notice what version of Ansible you are using (vs. the one used in the tutorial) as features change and also there have been some changes to the syntax to improve readability of your playbooks.
[0]: https://docs.ansible.com/ansible/latest/user_guide/vault.htm... [1]: https://www.vagrantup.com/docs/provisioning/ansible.html
Uses ansible + docker to setup and run a home server. Its feature-set is close to that of a typical FreeNAS setup in a home environment.
If you are concerned about Ansible SSH’ing in (which means you are concerned about any person SSH’ing in), you just do the standard SSH hardening.
Because you (or some intern hired a week ago) are 1 typo away from making a disaster.
For the record, security includes availability and this is an availability risk.