Hi, thank you so much for playing and providing feedback. You numbered these so I'll be addressing each in the same way:
1. D-pad up (or R on keyboard) is the button to swap between weapons. You can also hold it to dismiss your maggots. This is my bad, it's never properly tutorialized because the tutorial is already bloated as is and I didn't want to overencumber new players, but I should definitely tell the player about it at some point.
2. The game used to work like your suggestion, with maggots and weapons being fully independent, but it was too cumbersome to keep track of everything, especially in tense situations. I do plan for weapons with multiple slots in the future, so you'll be able to equip multiple maggot types on a single weapon and cycle between them while you're holding it. But playtesting has shown that this needs to be an opt-in thing for more experienced players.
3. Oops. I thought I squashed that bug for good, but apparently not. Thank you!