There's not a limit on the number of contacts you can add to Kinship, whether you are doing it manually or importing from your external sources (e.g., your phone's address book or a spreadsheet).
However, we recommend you start with a few until you get used to the app's functionalities. You can start by entering your most important connections - like your family members, closest friends, and frequent clients and business partners - and then you grow as you go down the road.