Hi Dave:
Welcome to you and your new fid. The only way I am aware of to sex the bird is DNA testing. It could depend whether you are in a hurry to know. I rescued a mistreated QP and the prior owners insisted it was a male. Imagine my surprise when Chico became Chica as she laid an egg in the palm of my hand. Based on that, I'm really sure she is female since I hear the males never lay eggs.

In fact, my obsessive, broody little girlie is sitting on a clutch right now.
Feeding lots of fresh fruits and veggies is good as well as dried fruits and veggies. You will find several threads here on feeding. Chica gets some pellets, a few squash or pumpkin seeds, almonds, bananas, apples, greens like lettuce, chickweed and broccoli, carrots both raw and cooked, mixed dried fruits, and treats like a couple of cheerios or a bit of cracker, a teeny bit of scrambled egg or cooked fish or chicken, and when she is really good a few hemp seeds. You need to keep the seed content of your fid's diet really low as seeds are high in fat and these birds are prone to fatty liver disease. She loves cooked corn and peas, edemame beans, squash, pasta, rice and many other veggies.
If you read the prior posts on what your fid absolutely cannot have like avocado, chocolate, etc. and try all the other low fat and low salt alternatives you will find he or she will eat a huge variety of foods.
Best of luck with your new boss whatever you decide to name her or him.
Lizz and Chica the wonder bird