Hey there! Let me see if we can answer this properly:
1. Packaging. There should be a way to package your RMMZ game from within the engine. We highly recommend clicking the "include RTP" (or whatever it is actually labeled for RMMZ) check boox so that there is less of a chance of things being excluded. That should work. If you are having trouble, someone one our Discord Server should be able to help more in depth: https://discord.gg/HfzupW
2. Game Donation on Itch.io. Although we haven't uploaded anything to itch.io, it's probably best set this to $0. You can always change that after the game jam. Just don't do anything to stop people from downloading and playing the game during the jam, please!
Let us know if you have any other questions.