[David R]

I have used nuts and bolts for hinges. They will seize from rust, otherwise it works.

1/2" pipe and 1/2" bolts for king pins and spindles or tie rods.

You could drill the threads out of a 3/4 nut and use a piece of round stock. Weld the nuts to the frame.

Most nuts have zinc on them, don't breathe the white smoke.

For the deck 11 gauge is plenty I use 10 gauge in small dump trucks. You can also use wood with a tubing subframe.

The bigger the wheels, the easier it will pull or push.

Looks like a fun project.

David