In Adobe Audince Manager, The segments created & qualified on the basis of hits. However, There are always possiblities of overlap among the Segments. This entriley depend on the segment logic as the mass segmentation may overlap with your niche targeting. For your reference, please see the help doc...

Hello @user42825, Please try using Adobe Developer mode & See below mentiioned restful APIs option. https://experienceleague.adobe.com/docs/audience-manager/user-guide/api-and-sdk-code/rest-apis/aam-api-getting-started.html?lang=en

Refer to this discussion  - https://experienceleaguecommunities.adobe.com/t5/adobe-experience-platform/migration-steps-for-cdp-different-system-aep/td-p/445174

@EdwinSusaiamul  Please explain which CDP you are using at present ? Each CDP have different frame work. However, you may refer to the below method. Make a data architect plan of all your source of data that how it is going to be on boarded into the AEP platform. Things like, data point, data type, ...