Not really suggesting anything, you do what you feel works best for you, just helping you brainstorm by throwing options at you.
You could go either way and likely achieve the same results, there are some downsides in accessibility with no control res, but you have no pipes leaving the box so no potential for leaks.
you should be fine to use the 27gal with the 38 if you really want to reuse stuff, but id probably go down to a 17 or maybe even a 12 to save space and water. You just need something that youre able to maintain the same water level as your inside res. Ive seen guys that use a single 10 gal bucket for a 16 res system.
Ive actually been considering down sizing my 55gal control res to a 27. it only gets like 8" of water in it so its complete overkill even for my 12x17gal res system.
I would personally stay with a dual 27 gal system like
@JSB99's with 2 plants each in your space though.