I made a similar bench, back when I had a 1 car garage (now no garage
) but I used all 2x4"s it was a tough bench, also very cheap to build. when I moved out I dis-assembled it, and my father in law wanted a few work tables, so we used the 2x4"s and made 3 tables total, he bought some plywood for the tops. so it was able to be re-used.
the ultimate bench in my opinion is the one my dad has in his shop, all metal. he has a 30x30 shop but is 2,400 miles away.