You can order as many things as you like. My guess is they weren't ever added to your cart, or perhaps your session timed out. What is your e-mail address you used to register at the store with?
This was a PM response to me from Armothe once when I asked about 2 items not being in the order (kinda glad they weren't though, seeing as the Green Powered Assault Commando armor came out and green was the favorite color of the person I was getting those 2 items for as a gift), but it's the "session timed out" part...because Armothe said:
If you log in and add items to your cart they should never be removed for any reason unless I deem it necessary to clear out shopping carts via admin. Keep in mind though that the products arent actually removed from inventory until you check out. Thus, it is possible to have an item in your cart which sells out while you are shopping for other items, and when you update your cart it disappears.
The old order form was nice when it was 20 items - imagine how long it would be today! I know most of you are used to the way BrickLink does things but that was a custom written application and I've never been able to find anything vaguely similar other than PayPal's cart....and I don't like PP cart. I don't think the BF store has a way to generate an order form and keep a connection to inventory - I'll keep checking though.
don't those two conflict?