Use a 4 layer PCB or even better use copper sheet only, 1 turn per layer, increase the frequency to 350kHz. I made this kind o transformers professionally the size you are using is good for over 300W.
Yes I forgot to mention it but the other reason I made the single layer PCB was to reduce the parasitic capacitance across the primary. In general also between primary and secondary it can be somewhat high depending on the distance they have between them.
Also! Instead of a single trace you can draw double trace to decouple by a little the parasitic capacitance, but i don't know if this technique worth the effort.
Yes definitely, although one should keep in mind that the inner layers are more prone to overheating because they're not in contact with the air. Also, they're more expensive.
It's just a simple opinion - it's not a tip - what if you completely eliminate what's in the middle - and the part of the wiring that is outside (those external outputs that can be seen in this video) should be completely covered by the magnetic core - in theory - that voltage transfer from the primary to the secondary is done by magnetizing the core as strongly as possible - by making that hole in the middle - you make a "magnetic field obligation" towards the outside of the coil - it's just a simple opinion.
