i would imagine the flyback is ok if its supplied by him, what you did with the metal part is correct
bu508af should be full plastic package and therefore does not need insulation sheet but would require heatsink compound- Mouser are a trusted supplier so I would seriously doubt they would stock any fake components
test the b+ by dummy load on the collector, you do not need to isolate any other pins, you should get a good solid glow from the lamp and the b+ should read around 130vdc. You can also test your 16v and 24v
if all tests ok then remove lamp and use diode test to see if you have any shorts on the collector to ground