Thread the rods through one of the legs, then set the leg flat on the table. Insert dowels into the dowel holes. Place the matching stretchers into place. Put dowels into the dowel holes at the top end of the stretchers. Place the other leg onto the threaded rod and settle it down onto the dowels. You'll probably have another opportunity to whack away with your rubber mallet.
I used the factory edge of the half-panel of hardboard as a guide for cutting the ply. I wanted to cut a 5-1/2" strip, and my saw cuts 4-1/2" from the edge of the shoe, so I wanted the edge of the hardboard 10" from the edge of the ply. So I set my combination square to 10", and used it to mechanically set the distance. Hint - if you need two things to be precisely the same length, try to avoid measuring them separately. Use some mechanical mechanism for setting the distance.
If you decide upon construction lumber, you want kiln dry lumber. Green lumber will warp on you as it drys. Dig through the stacks and pick out the straightest, cleanest pieces. Generally, the boards that are sitting loose on the stack are those that other people left behind, as they sorted through looking for better. Be prepared to move them out of the way, and to dig down to the better stock. Be nice, though, and put everything back when you're done.
This table top is also made from the hardest wood out of any manufacturer we reviewed: oak. In fairness, this can be both a blessing and a curse. The oak wood is extremely durable and noted for its lack of a porous nature. This means the top can withstand plenty of abuse from tool and workpieces. Moreover, you will not have to worry about liquids like lacquers and stains from being absorbed into the top. That said, the hard oak can also do a number on tool sharpness, dulling them prematurely if they are not carefully handled.