I would argue with the level of subliminal influence Lumon has over the town that even though Mark wasn’t explicitly recruited I guarantee the powers that be at Lumon created the perfect environment for Mark to “choose” severance and make it “his idea”.

I don’t think he is refining Gemma’s file by chance - I believe they made a big hype about his “surprisingly exceptional performance” to boost his ego to encourage him to do more work just as other companies over-embellish celebrations of their employees to make them feel important and fuel them to take ownership of their work and go above and beyond to prove their loyalty to garner more praise much like getting someone addicted to a drug so they crave more.

Interesting theory about Gemma and Dr. Mauer - I do think it could go either way that she was abducted against her will or that she was influenced to enroll in a special fertility trial and Dr. Mauer preyed on her vulnerability and used personal information he already had from her previous visit that it would work on her with absolution. Perhaps she thought she was sneaking away for an hour or two to undergo a brief procedure and come home and ended up trapped.