Yeah, it's definitely disorienting to start with. The inbox error is referring to a "DM" inbox. You can enable those by clicking the "Inbox" chip on those relay cards. That won't fix note discovery though — one thing you might try is make sure you only have 3-5 read/write relays. Any more than that is redundant, since they're more about signaling where other people should send/find notes than instructing coracle where to look for specific ones (coracle should be mostly doing that automatically).