If you decide to go the official route, here is how you can "develop" your own custom offline collection:
You can still download songs to your device for parties without Wi-Fi. If you decide to go the official route,
If you have a Premium subscription ($9.99/mo), you can sync up to 1,000 songs to your device for offline use. you can sync up to 1
Downloading copyrighted music without authorization is a violation of copyright law in many jurisdictions. If you decide to go the official route,
While the economic impact is on the industry, the technical risks fall on the user. The search for a "complete pack" is often a vector for malware.