Questions 'bout my sewing table! Sewing Machines Parts and Sales in Los Angeles

So my ahmahzing and eencreedible husband made me a big-ass table out of the top of a half a ping pong table. I was going to cover it like an ironing board because the edges are a little rough and that would just be hella convenient.

Here’s my pics:

Now, as you can see, the Ironing material is only 45″W, while the batting is 54″W (the table is 54″ x 60″), so I’ll have to seam the fabric somewhere.

Ok, my questions:

• Where would be the best place to seam the top layer? I could just seam the very edge, like it’s laid out; but my instinct says to center the seam over the center of the table. Then it could be centered either the long way or the short way.
• Should I wash both items before sewing? Again, I assume the answer is yes, but I don’t want to damage the batting, so I’m double checking.
• How do I “square” batting? I don’t want pulls or drags in the material, so I’m going to square up the ironing cloth, do I do something to square up the batting?
• I was going to quilt the two pieces together so they move together. I got a brilliant idea to quilt them in 1″ square grid to make blocking and pattern making easier. Am I fooling myself that the grid will maintain its integrity and/or anyone is capable enough to sew 3240 squares perfectly square?
• My other thought is that I could draw the pressing lines on the fabric, but then I’d need a recommendation of what type of fabric marker to use that won’t bled onto fabric when heated or steamed.
• Speaking of steaming, the ping pong table is press board. I’m assuming I shouldn’t use steam directly on this; that it would be for dry-pressing only. Confirm or deny?

I do have a decent ironing board, a cutting mat and a rotary cutting mat, so it’s not like this has to be the alpha and omega of sewing table solutions, but I figured if I was going through the trouble of making it, I should make it as AWESOME as possible!

P.S. Can y’all notice for a sec that he added electrical to the table? And there are three recessed drawers and a platform. The whole thing is on casters so I can move it whenever I need to.

Though, it’s so big unless he disassembles it, I won’t be able to take it with me when/if we ever move. :’-(