I have finally gotten in which is great, but I did see that it says the more ranks you level up, the more items show up in the BB point shop. Exactly what rank does that cap at, and new items stop showing?

level 20

Oh wow really? I got to there in two days, awesome :)

yep. It's difficult to drop levels, you have to have in mind going there and refusing quests on purpose. Most items you can buy from the Blue Building are cheaper to buy from users with sP than the cost of the BB points that you quest for. This is because they want the Achievements more than they particularly want anything that's gettable from the Blue Building.