Connecting Thunderbolt 2 Mac to Thunderbolt 3 Display, what is the maximum resolution@100hz , will USB 3.0 work? I own a MacBook Pro 15&quot; 2015 with a Thunderbolt 2 port.
I have recently bought a Samsung cj791 Thunderbolt 3 monitor
(3440 x 1440 @ 100Hz; 85W Power Delivery)
I plan on connecting the monitor to my Mac using: a) A Thunderbolt 3 male to Thunderbolt 2 female adapter and b) a regular Thunderbolt 2 cable
These are my questions:

Will this work at all (I have read it didn't before High Sierra)?
Will I be able to go up to the full 100Hz this way at the full resolution? (Another post said TB 2 works with 4K @ 60HZ which is the same data rate - a little more even)
I have read connecting 2.0 USB peripherals through the monitor is possible, does TB 2 also support USB 3.0 throughput?

Thanks.
Yes in general. I use the same adapter to run all manner of USB-C and Thunderbolt 3 displays from 2013 Mac Pro and MacBook Air and Pro from the same era. You don’t get any extra resolution than the Mac could drive originally using adapters that shipped when the Mac in question was brand new.
I’m delighted with 5k displays running over the Thunderbolt 2 and all USB and Thunderbolt hubs I have tested work at full Thunderbolt 2 speed. Since USB-C and 3.0 is less speed than Thunderbolt - they all work fine in my experience.