Wall for scale

While this is "technically" DIY, I feel that this may be a bit too niche for this group. Also I just threw up in my mouth a little.

I've never installed ventilation in a cabinet, but I would drill a bunch of holes in a circular pattern similar to how it looks on the back of some computers. Drill a few more for the mounting holes and use screws to mount the fans. If you don't have a drill, you should be able to cut particle board with a utility knife.

Our floor tends to buckle a little in the summer, though not as much as yours. It makes a lot of cracking noise when you walk on it. If the contractor is offering to pull it up and redo it for free, then I would let him, and have him add the 1/4 gap around perimeter. If not, then cutting it yourself might help, although it will be a pain.