Will provisioning the APM module affect the existing BIG IP config?

Max,

First of all enabling a new feature in your F5 requires you to reboot the appliance in order to re assign resources.

The included APM module will not cause any changes to your existing enviroment, it will only enable you to use the "Access" tab in the left menu where you can set up all the authentication, vpn, sso, among other configurations. Most of the time you have to attach these configurations to a virtual server in order to work, anything will be enforced and also there is anything pre configured out of the box on the APM module other than common templates for authentication.

Regarding hardware, make sure that your appliance is ok in a resource utilization manner, if your LTM module is struggling just don't enable it.

It would be a good idea for you to test these steps in a lab enviroment just to get you more confident and show your coworkers that it will not affect anything at all, you can request a free eval license for 90 days in the F5 webpage.

Regards,