They won't benefit with a new tank very much. They would help once your tank is more aged and is growing algea. You could buy one now and feed him algea wafers. If you want an animal that will clean the bottom of your tank for now, like the uneaten pieces of food, try a snail (mystery or apple), or a dojo.
A precaution, dont buy a common pleco, there have been many horror stories dealing with those and members goldfish.
And
CONRATS on your new tank!