Hi all, need some help on how to safely mount TV / recommended hardware and installation location on wall.

My predicament:
* I have a pretty heavy TV (85 pounds) and mount another 25lbs, and trying to get mull-motion/articulating mount safely on my wall.
* I had my contractor put in 1.5" of plywood attached to two metal studs where the mount would be installed on the drywall
* To center the TV with my couch, it would involve putting one end of the mount into 8" thick concrete/masonry while other half on the drywall

I'm not installing this myself (will have another professional do it) but I'd like to make sure I understand the recommended hardware/approach.

Couple questions:
1a. If the mount is installed partially on concrete and partially on drywall, any major issues with that?
1b. I've heard toggle bolts recommended. Would those be drilled/installed where the stud or into the plywood backing
2a. If want to move the TV/couch over to the right so that the mounting bracket would be fully on the metal studs, is this ill-advised or does the plywood give it enough support?
2b. If the bracket supports stud spacing between 16-24" and my studs are 24" apart, should holes be drilled into the plywood or drilled into the metal studs? I wasn't sure if the plywood is meant to the be location where the mount is attached, or does mount still get drilled into metal studs and the plywood helps with weight bearing.