Thanks to all for the helpful feedback. I think we'll stick with the tight window, book the FastTrack through immigration, and hope they're efficient with the bags. I did look at this flight history and it generally arrives between 5 minutes late, and 30 minutes early--so that's good.
Yep, I second Real. I've got a decent touring helmet that's safety certified, relatively comfortable, and was only like 2-3k baht. The shape may not work for all so you'll want to try to fit first if you can.
Thanks all! This will be at the office in Central Festival Chiang Mai so probably just easy enough to swing through and ask on a free day anyway... or at least not a big deal to have to go back a 2nd day if they need all present.