Tubs should be stored in the cool and dark for about a year before use, this helps the rubber to "cure" and makes the tread more resistant to flints and the like.
Always use proper rim cement, I have seen disasters with people just using tub tape, it simply does not work well enough. Remember always to score/roughen the rim bed, paint on a layer of adhesive, leave to dry for a day, paint on a thin layer, fit tubs. If you have not done this before, have hand cleaner and a bit of solvent to clean the rims up when the inevitable happens and some adhesive ends up n the outside! The tubs mentioned, at that price, I'd get as many as you can afford! Planet X does seem to get some good deals. You won't go far wrong with CX's.