Wood choice and delivery
This project use minimal tools, so it is important to have the minimal amount of work to do on the wood. Chose one by one the 2x4 to use. They should be very straigt, with regular wood fibers, and minimal amount of knots.
Ask the wood seller to cut to length the 2x4that are going to be used for the bench top. For the frame you can cut it yourself.
Besides the 2x4, I ordered one sheet of OSB cut in 3. OSB is cheap, sturdy, and generally useful.