Can't attest to US delivery times but Ali express std delivery option is 10 days to UK. Many suppliers on there display a choice of different postal services.
Sturmey use 12mm in their single sided drums which are very popular in velomobiles for their easy remove-ability and I'd agree with using high tensile 8 grade bolts. As to wanting the strongest, you'd only need 20mm If exceptionally heavy or you expect to hit a lot of potholes or go off road. It's the easiest thing in the world to go heavier on the build and then (exaggeration) it's the hardest thing in the world to actually pedal it. If you do use 20mm hubs I'd either shim it to use a smaller bolt or like Brad shows in the instructions build a smaller bolt up with weld to save weight.
Most BMX over in the UK use 3/8 axles. It's the higher end that use the 14mm in my experience though they're hardly scarce. There's also quite a number with one 14mm and one 3/8 as std on some bikes though I can't remember which way round (front / back) that goes. Different markets may well be different, possibly based on the average user size and expected use in that market.
How do you post a pic on here. Or can youTrying to find the wheel hubs for the front wheels. Everything I’ve seen on Amazon and eBay are front and rear sets. I don’t need rear hubs. Does anyone have any idea where to buy front hubs. Preferably that will accept disc brakes. Thanks in advance