OK, that helps.
A 5 hour party is a long party, so the guests will eat about a meal's worth of food-
Peel and eat shrimp- (? lbs)
cocktail sauce- how much?
The most hard to manage item will be the shrimp. People are greedy about them- some will take a plateful. I would put them with the chicken, so people will take some of that. too. Also, given the difficulty of the shells, unless this is a sit down party where people can free both hands, I suggest you get peeled, tail-on shrimp. Allow 1/4 cup of sauce and at least 3-4 ounces ready to eat shrimp per person, if you premix the shrimp and sauce together, people eat less; serve in a bowl place inside another bowl of ice, and put out only 1/3 the first hour, divide the rest into 3 and put out each part the next hour. Frozen mussels are much less expensive and could be used for part of the seafood choices.
Bacon wrapped scallops- (? lbs, how much bacon do I get?)
Scallops vary a lot in size! 2 ounces can be 1 scallop or 4! It takes about a half slice of bacon per scallop, you should allow 3 large or 4 medium scallops per person, get thi-sliced bacon, and calculate it after you see the size of your scallops.
sausage stuffed mushrooms (how many mushrooms per person, how much sausage do I get?)
You want two to three mushrooms per person, depends on size, and 2 ounces raw chicken sausage for the stuffing.
chicken satay (how many lbs do I get?)
Allow 4 ounces raw per person
Peanut dipping sauce- (how much?)
Allow 1/4 cup per person
I suggest you add one major vegetarian option, I would do hummus or baba ganouj with pita chips and dipping veggies
I would also add some fruit, at least grapes, 3 ounces per person and cheese (some could be logs, balls, or spreads), 2 ounces per person.
We will have about 3 to 4 other prepackaged items
Allow at least 2 bites per person of each one.
Watch out about oven space! It looks to me like you may have too many items that need to be hot for one oven to manage.