Hi Robert,
Let me try to answer your question as I also just got into ansible for the past two or so weeks.
Ansible is agentless therefore you don't need to add anything to your existing infrastructure in order use it, this is one feature that has really made me dig in more into it. SSH access for me, is all I need.
My starting point was to split my hosts file into various catergories ( webservers, dbservers, mails etc) of the existing infrastructure I am managing. I have since then run simple playbooks like getting os details using the "setup" module.
I have had a good start with it and I already foresee so many possibilities.
Regards,
David.