I got my top panel from woodpanel.com.my.
If I have to diy, I will use ikea metod worktop but that is more expensive.

The cables between wall mounted TV and cabinet are hidden by soundbar.
For other cables (woofer, gaming console), just mount a 1''x2'' pvc wire casing below the cabinet. It won't be visible from front.
Eventually, I didn't hack the wall to hide those cables.

Yes, my contractor did the same. Pvc pipe easy to get the cable slide down.