Thanks for the questions! Happy to see the community engaging in this proposal.
We chose 11/12 NFT badges, representing 90% completion of the Odyssey 2.0) as the airdrop threshold as a way of only rewarding users who have been highly engaged in the Odyssey. Each time we lower the badge threshold we increase the number of less engaged users that will be rewarded.
The first Arbitrum Odyssey caused a meaningful increase in transaction volume which resulted in the Odyssey having to be paused due to an increase in transaction costs. I’ve found this Dune dashboard which has some stats from the first Odyssey. https://dune.com/springzhang/arbitrum-odyssey-event-tracking
The protocols that ended up being in the Odyssey 2.0 was a collaborative choice, we (Unstoppable) reached out to the first few projects and then asked them which other builders they thought should be included, this process resulted in the final list of participating protocols.