Yes, you can order Snack Shack food and quantities shouldn't be an issue. Our server brought us funnel cakes for 8 a couple years ago. And fwiw, I don't think it's a ridiculous problem.
Unsolicited opinion... the coconut crusted lobster sandwich from the Beach Club is excellent. Anyone in my family who eats lobster liked it better than the plain, MDR-style lobster.
You can definitely make that request. You can even request a specific number. They're all fine but if you're going out of your way to make a request, I'd choose one in the front row (farther out in the water) so you're looking out at just the water, not past another cabana. Really not a big deal but since you're requesting something anyway...
Enjoy the cabana!