RE: Trading Landorus ex, FA Colress, Hypno Laser, Catchers, Max Potions for Bulk!
Oh wonderful, good. Here's what you do for shipping:
Get a large flat rate box, pad the bottom with some plastic (can be bubble material, grocery bags, whatever, just a thin layer). Separate everything into piles of 100 (if it isn't already). Put all the cards side by side so that they're lying down horizontally. You should be able to fit 900 cards (or 9 piles) per row. Repeat this until you have 5400 in there. Put the non C/UC stuff on the top rows. There should be some space left over on the side (if you squeezed all the rows together). You can technically fit up to 600 more cards there, though you don't need that much space.
Print a shipping label online - it's cheaper than going to the post office.