I think you should think bigger. I have my main garden about 25 by 100 ft. which is only 2,500 sq. ft. There is only two of us, and I do not grow either potatoes or sweet corn, two of the biggest space hogs.
I like it relatively long and narrow for three reasons. One, it makes for less turning when you are plowing it the long way with bigger equipment. Two, you can run your populations crosswise the whole width of the narrow dimension in a solid block, and it makes it easier to rotate crops to different places from year to year. and three, it makes watering easier, my reciprocating sprinklers just cover the narrow dimension, and I can move them up and down the long dimension as needed.
I have 30 running ft. of onions, 20 of strawberries, 20 of the cole crops such as cabbage, broccoli, etc, 12 of the root crops, which does not include potatoes. You can see the ground is used up fast. For your situation I would say 4 to 5 thousand sq. ft. would be advantageous.
For edging, what I do is not have a standing wood edging, but one that is buried. That is to keep the grass roots from creeping in. A 2 X 6 or 8 buried so its top is flush with the top of the ground will keep most creeping grass out and give you a clean edge to mow on. A standing edge will let the roots grow under. You will want to use treated, and seal the overlaps, corners, cracks and knot holes well with silicone seal. The grass roots will find their way into any opening. Adding a few inches of topsoil and compost really should not require sideboards.
You will want to plan for the placement of your perennial crops such as strawberries, asparagus, rhubarb, and any perennial herbs so they do not interfere with your tillage.
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