Can I bake a cake in a 9 x 13 baking dish and not just the metal ones? I want to be able to make two 9x13 cakes at once because I don't have the time to wait for the 1st 9x13 to cool and take it out.

If I can, will the cakes come out different?

Yes, you can. Just lower the temp of your oven 25 degrees F.

I want to be able to make one 9x13 cake in a metal pan and one 9x13 in a glass dish at the same time. Is that possible? Do I lower the temperature then?

Yes, you can bake them both at 325 at the same time, but the one in the metal pan will likely need a few extra minutes of baking time.