Gosh, that is a lot to ask of a one year old to party all day! For one thing, the first birthday party is NOT for the one year old, the child would probably be happier reading a book with you than to have a WHOLE BUNCH of people in her face expecting her to be excited for a couple of hours. The first birthday party is for the parents and family to celebrate the precious life that you have been given.
First, make sure that there is at least one person who can attend to the needs of the birthday girl any time she needs food, nap, time to chill, etc. Have a bunch of open ended activities for the kids. Some kind of craft that will work for any age. Something that has worked great for us is decorating paper bags to be used for the pinata. Have lots of craft supplies, like stickers, crayons, feathers, pom-poms, etc. The big kids and little kids will enjoy this and then they get to put their treats inside.
have a fun party (s)!