Cool project!

A lot of this is general snake information. That I can give as I never bred ball pythons.

I can come over as abrasive, too. I'll bear with your if you'll bear with me.

1. The only lock I ever saw in my ball pythons did not result in any eggs. So it happens, but I can't give statistics. Properly cycling the snakes (as I did not) should minimize that sort of thing.
2. YouTube video? Basically, use a blunt probe and be gentle.
3. IMO, start small. You choice may be different.
4. a) No opinion.
4. b) Inside the tub. Check with a high school science teacher about where to get scientific thermometers with plus or minus 1 degree Celcius accuracy. Photo developing thermometers are also good.
4. c) By whether or not the eggs are dimpling.
5. Sure there are tubs that are too big. I use whatever size that works.
6. Each egg is sired by one male. But two or more males can sire a clutch. This can happen with human fraternal twins, too

Good luck!