Hi there,
Welcome to AAM community!
1) First thing you would need is ID stitching of your CDP's cookie ID with AAM's ID.
Some data providers/partners have an out of the box ID sync with AAM, so you don't need to implement anything. Just, contact Adobe to enable the ID sync if that data provider/partner is listed here:
https://docs.adobe.com/content/help/en/audience-manager/user-guide/features/destinations/device-base...
https://exchange.adobe.com/experiencecloud.html#search
If that CDP is not listed here, then you will have to implement a customer ID sync on your web properties. So, whenever a user will come online their CDP cookie ID gets stitched with AAM ID.
You can then onboard the selected CDP cookie IDs to AAM as offline data and create audience out of those IDs.
2) There is no additional fees to connect any platform with AAM. However, uploading the offline data incurs billable server call, i.e. one server call per one record row in offline data file.
3) You cannot do such customer journey analysis in AAM. You have to rely on any web analytics tool like Adobe Analytics or AEP for that.
Thanks,
Varun Kalra