Hi kaleb,
Ultimately your best bet is to take a look at the CRL (costume Reference Library) for the specific costume you wish to build. Match the text and images to what it is you are looking to buy.
Basic level is your first stop to get 501st approval, but you can certainly build from the outset with all the extra trimmings to make it easier when going for Expert Infantry then Centurion levels.
Most importantly is building the costume to fit you properly, that is what separates approval from have to make adjustments and changes to passing and gaining your membership.
Unfortunately, your link throws up a message " Oops! That page can’t be found." because you haven't separated them into individual links its just one big one.
Fix that so members to go into them and offer you feedback
As an example, things like the neck seal for R1 only has a basic stipulation, so there's not much to worry about there as long as it fits and conceals the neck properly.