The green twisted pair from the pilot light to the power tube is important as is twisting the rest of the 6.3v circuit. Twisting the pair of wires together allows them hum cancel. Keeping the 6.3v wiring away from the rest of the signal chain is helpful too. There are recent postings in the forum about heater circuits.
Larger gauge wire is fine, it’s harder to work with and fit into the eyelets and lugs. I use 16g for speaker wiring.
That’s “turret” board construction on my 2Stroke. I wanted to try that after a couple of eyelet board amp builds. I’ve built several turret board amps and would do it again. I like it better then eyelet boards because you can make component changes easily, attached more leads and the boards are fun to make. You can get turret board construction materials a lot of places, I get mine from Hoffman Amps.
Here is a better view of how the turrets stand off the board. This is from my 15w amp build.