Yes, of course! After all that hard work you put into making the costume, you deserve to enjoy yourself. Just be careful, your costume might be fragile.
Try Amazon, TJMaxx, Ross, Marshall's, or even a thrift store. You could also ask family, friends, or neighbors for one, or for the supplies to make one yourself.
You can, but keep in mind that the pillowcase will only cover the face. Use a whole bed sheet if you'd like to cover yourself completely. Just be sure to...
If you're pinning the sheet to the hat and then wearing the hat under the sheet so the sheet doesn't shift around and slide off your head, then yes, this...
Yes, gauze is an excellent choice for making a mummy costume! Get several rolls of gauze bandages or a roll of gauze fabric (about 8 yards or 7.3 meters) that...
Wear a wreath of olive branches around your head (Athena invented them). Maybe add a helmet or a chest plate for armor. Adding a shield and spear will help too.