Those are definitely things I'm going to have to fix, thanks. Getting combat difficulty down is hard, but I'll do my best to fix the early game! Although, did you try interacting with the mailboxes in the Desert World?
The world portals exist in all worlds, it's just that the only ones accessed in the game are dying ones as they're the ones the characters are actively seeking. World traveling however is rare due to the untold dangers of going into other worlds, and is mostly why Mr. Keepe is reliant the gang to retrieve artifacts. Outside of the story he ventures into non-hostile worlds or commissions explorers to delve into the more dangerous ones. It's something I wanted to show off in the game but didn't really have time for; I originally wanted to make an extra world that had a gang of explorers that got there before you and you would have to convince the leader to hand you the world souls (and to do some trading for Mr. Keepe's artifact quest).
Mr. Keepe places all the radios in the void and the one in Queen Uriel's land. The other radios were already naturally there for other reasons, though I honestly should make different sprites for these specific radios to show that it's not the generic ones Mr. Keepe is putting.