I have heard good things about both of those websites. Just make sure that you're considering the shipping cost when comparing online places to your LFS
Hermit Crabs and snails are the front line for your cleanup crew, they should make up the majority of the package.
You may want to avoid the sand sifting star if you're going to have corals later. The sand sifting star will reduce the number of pods
your aquarium produces.
You may also want to avoid cucumbers, some varieties turn toxic when they die or are very frightened. Be sure to find out and research the exact species if you're getting a cucumber.
A Nudibranch can be useful to target a particular pest, but in general one species of Nudibranch will eat only one very specific food. It will eventually starve if you don't find out what it eats and find a regular supply of that. Don't pay extra for one.
Shrimp can be very interesting and useful additions to a cleaner package. If you want a "cleaner" shrimp though, you might want to wait to add him when you have fish. If he gets in the habit of eating fish food, he will spend less time cleaning the fish.
Emerald crabs can be invaluable if you develop bubble algae, they are one of the few critters that control it well.
Conches are interesting, but might get a bit cramped as they grow. A fighting conch will grow to 4". Pacific conches are slightly smaller.