Fill out every field completely. This is exactly what gets written into your file's metadata — title, artist, ISRC, artwork, everything. Pay first, then submit.
The $300 "We Get You Your Own Code" tier includes your one-time USISRC registration fee — we handle the registration through the US ISRC Agency on your behalf, so there's nothing to pay separately. Your code is registered in your name and belongs to you permanently. After that, all future releases only require embedding or mastering + embedding. USISRC Agency (for reference only — we handle registration for you)