6 PM Friday night is a perfect start time. Pizza and cake and presents right away when everyone arrives. You seriously do NOT need to plan very much-- they will amaze you at how well they can entertain themselves in a group that big- especially if the girls already know eachother. I do recommend that you have a craft for them to do-- go to a craft store to get some ideas-- something easy that they can be creative with-- like you can buy white t-shirts (or pillow cases) and let them decorate with fabric markers or even just use colored sharpies (put cardboard or a magazine inside so it doesn't bleed through). One year I found canvas bags really cheap at the craft store and they decorated those. I would stay away from fabric paints or you'll end up with it on something you don't want it on (carpet, furniture, someone's clothes) and you can't stack them because they take forever to dry thoroughly.
Plan to be flexible. Once she opens her presents, you may discover she has a new game or craft kit they want to do together. Have one or 2 fall back activities that you don't care if you get a chance to do or not, like a board game that a big group can play. If your daughter is into make up and hair, you can let them do that for a while-- my daughter and her friends aren't, but she has come home from sleep overs covered in marker because the girls decorated eachother with markers! They actually have body art markers if you can find them-- I suppose they are just non-toxic and wash off easily?
Set up their sleeping bags/blankets/pillows all over the living room so they can claim their spots, then let them play a bit longer. When you are ready for the party to wind down, that's when you pop in a movie. Don't expect them all to be happy about the same movie, or want to sit quietly and watch it. You never know.
Make clear rules about not messing with kids who fall asleep first. I know that was a fun part of the sleepovers when we were growing up, but it just seems so cruel and I have heard of friendships that have been strained over feeling like they were singled out and picked on (drawing on girls who are asleep, sticking their hand in water to try and see if they'll pee, splashing water on them so it looks like they peed, etc.)
The next morning, have an easy breakfast like milk and juice and donuts (unless you LOVE to cook for a large group, in which case pancakes is always a hit). I'd end the party at 10 or 11. We usually let one or 2 very close friends spend the day, but it depends on the group dynamic if you can get away with doing that without hurt feelings.
I don't know the age difference with your 2 daughters, but you may want to allow your other daughter to invite one friend of her own.
My son and daughter are only one year apart in grades, so all of their friends know eachother. This past summer, my daughter was turning 10 and wanted a boys-against-the-girls mall scavenger hunt party, so I actually had a boy/girl sleep over with 5 girls and 4 boys. I made them all sleep in the living room and I slept on the couch! It was a blast.