You know those little bumps on their underside where they pee from? When they are females, the bump is right under their anus. Pretty much touching. When it is a male, it is quite far away from the anus.

Hamster/gerbil food is fine, don't worry but I would supplement it with other things, like fruits and veggies, and other things you might find in your house, like cereal, oatmeal, ricecake, and other things that are fine to eat Dandelion and clover are also okay to eat.

When I was teaching my gerbil to drink from the water bottle, I picked her up and pushed her nose against the ball lol.

When taming it remember to pick it up as much as possible so it gets used of it. But only pick it up in your room where it's quiet, and once it gets used of being held, you can bring it into different places.

Are you going to quarantine it? You may want to, just incase. You wouldn't want your hammies to get sick