They most definitely can read triple layer discs as they are commonly used for 4K Blu-rays. And when a drive can read TL-Blurays it most likely also can read QL-Blu-rays just fine. However, those are rare so I would suspect a 2x TL release.

A single Quad layer Bluray could fit the entire game, but not a ton of PC users have an optical drive, much less a Bluray capable one. A microSD card or USB drive might be more viable these days. A 128GB costs less than $10. When you want to stick to DVDs you would need either 27 (DVD-5), 15 (DVD-9) or 8 (DVD-18). Multi-DVD releases are definitely a thing. Star Wars Battlefront comes on 4 discs. I suspect they would opt for a DVD-9 release as this allows you to print artwork on one of the sites and you likely need a few extra discs as you cannot use all of the storage for data. So we talk about a 16-18 disc release. ~22mm (7/8 inch) of DVD goodness.

It actually does. Blurays go up to 128GB and the game needs 125GB.