The max APY for EURx is 12% which is the same as the max APY for stablecoins. The difference being that you can earn the maximum stablecoin rate without a fixed term. So definitely not a bad idea to use stablecoins instead.
Yes, provided that at least 10% of your non-NEXO portfolio is in NEXO tokens (requirement for Platinum).
Check their loyalty tiers here: https://support.nexo.io/hc/en-us/articles/360017445559-Nexo-Loyalty-Program-Explained
Also this for the new rates starting from July
You can check some of them here https://nexo.io/blog/a-new-yield-program-is-coming-to-our-earn-interest-suite-in-december, but I would recommend to check them through the app - "My Profile" > Loyalty Levels > (scroll down) Breakdown of savings rates