Hi truB!
ACS won't be a topic to worry about. The AAA stuff is done with local credentials on the router for the CCNA-Security. From Cisco Learning Network:
"Implement AAA on Cisco routers using local router database and external ACS
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Explain the functions and importance of AAA
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Describe the features of TACACS+ and RADIUS AAA protocols
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Configure AAA authentication
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Configure AAA authorization
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Configure AAA accounting"
Mostly be aware of the theory of TACACS+ and RADIUS and be able to set up aaa on a router without accidently locking yourself out. (reload in 5 is a good thing to implement before you do aaa new-model and forget to place your local database and define methods for the VTY and CON line...NOT that I'VE EVER locked myself out of a box with aaa

) Or you can schedule a kron job to reload the box or use embedded event manager...but reload in 5 is easier!
For the part that refers to the ACS, just know what command(s) are necessary to tell the router how to contact the server (host and key) since it's all pretend.
This is very similar to some of the labs I've done for my CCIE R&S where the actual servers don't exist but I have to set up the routers/switches as if the servers existed (WCCP, CNS, etc.) Mostly just typing exercises...
HTH