@Nick would like to meet a decent amount of people....
it's a contacts-like app, so I need to be able to bring in a decent amount of data to properly test it.
Sounds like a job for randomuser.me. This is an external site, am not proving a link.
But it allows for different address types (Canadian, European, 'Murca) It has long and short first names and family names. It generates fake email addresses, phone numbers, id numbers, and you can also get random photos.
There's many options, download test data for testing whilst building your interfaces. Also json interfaces for when you're ready to test your network code.
Another popular option is mockaroo.
If you're asking for best practices, I'd think you want to first focus on your app's functions. Get it working smoothly with a set of data that you have on your device. You can also set up a fake data service on your dev maching. Towards the end, you can link to external data sources and pound your network code.
Some of all of this advice might be ramblings. Good luck! Please return here and share you trials and victories.
Keep Coding