Yeah I think you can use that code on the UD site to buy stuff. Never tried myself but I have pulled those fillers before and just used them as extra security when posting cards in bubble mailers. They are great for that.
Congratulations on your first box break champ! It's a dangerously good feeling isn't it?
The cards that look similar to base but are numbered on the back are parallels #/299 - gold, #/99 - copper.
there are also blue #/49 and black #/1!!!
The rookies are numbered depending on their card number; 101 - 110 #/150, 111 - 125 #/799, and 126 - 149 #/399.
I've got a fair few base cards from this stuff if you want to have a go at putting the base set together. there's 100 cards in the base set (rookies are numbered 101 - 149 and are not considered part of the "basic" set) and you've got the 3 top values (mj, lj, kobe) out of the way already!
It's a nice looking set and it goes some way to getting a bit better value outta your box!
hope this helps a bit, send me a pm if you want any other help...