Yeah, would work for engineered hardwoods.

Don't do this. Laminate floors are "floating floors" . They are not attached to the sub floor for thermal expansion/contraction. Cutting the tongues and grooves off will keep it from locking into the pieces around it. Gluing the replacement piece down will keep it from moving with the rest of the floor. It will gap or buckle eventually.

Drilling a hole in the flange won't cause any structural issues in the sink, if that's what you're asking.

If it wasn't undermount, I'd recommend releasing the sink and popping the silicone, then putting a block between them to drill the first hole, but that's a much bigger deal to do with an undermount sink.

What you're suggesting is probably your best option, but understand that there's a good chance your diamond bit will be headed for the garbage as soon as it touches the steel.

If it's only a half inch hole, a hole saw may not be the best choice. I'd probably drill the steel stepping up to ½ with carbide drop points.

This isn't necessarily true. Quartz is typically cut with a diamond crusted abrasive hole saw, preferably a wet cut. Attempting to cut steel with the same bit will destroy the abrasive. You might make it through, but the (very expensive) bit will be ruined.

On a normal switch, there is no neutral terminal. The three connections are for line in, line out, and ground. Neutrals are bridged in a standard wiring situation.

Not to operate, no. Some are saying codes require it now. A "dumb" switch only interrupts the circuit. You could wire the neutrals to the switch instead of the hots, and it would work exactly the same. Shouldn't because changing a light bulb would then carry the possibility of electrocution, but could.

Believe it or not, the neutral carries exactly the same current as the hot, when connected in a circuit.

That's not mold, it's duct sealant.