If it has a 5/8 axle it should work.
It supports loads up to 175 lbs for each wheel.
No they are solid rubber wheels. They are very stable
Sorry, not sure exact width, but I looked at mine and would estimate the hub is at least 2 1/4 inches wide. Visually it appears only slightly narrower that the wheel and the wheels are almost 3 inches wide.
I believe that what you refer to as a “split washer” is the same as a lock washer. They just make different types of locking washers. I would use either type of locking washer along with the hex nut.
A hand truck is another word for wheel barrel. You mix cement in wheel barrels, carry dirt, planting soil, sand, even heavy stuff like cement blocks or bricks. We even use ours for hauling wood from the woodshed to the house to transport inside for a nice fire.
You need a 5/8 in. wrench.