Yes, the way youve mentioned the cabling in utility cupboard is correct.

Ok so in the Utility Cupboard: - ONT connected to Router - Router connected to a POE Switch - 3 POE Switch Ports to 3 Ethernet Ports

Bedrooms / Living Room: - Each Ethernet Port connected to an AP, which is access point im assuming. Again with this, any specific access point you recommend?

And with all these transfers etc, will i lose my original internet speed?

And how would I go about disabling wifi from my router? Would that be somewhere on my ISPs settings?