To answer the question, you get all the kit at once; the combats all the other kit for the field, plus your dress uniform. Incidentally, for the Navy types, this means we have about twice as much kit on diplay during inspection. Lots of ironing.
But you really don't need any extra items, in fact there is no where to put it, and odds are you won't have any access to your suitcase anyway for the first month. You get issued towels and everything too, so ignore the joining instructions (unless they get updated, they tell you to bring a lot) and just bring 1 set for the first bit until you get your issued stuff. Also, for the first couple of days before you get your issued gear, they'll have you marching around in civies, so make sure your dress shoes are comfortable. Aside from socks and underwear, you only really need enough clothes for the first few days and the odd weekend.
When you do actually get there, if you do get the chance, pick up an extra pt tshirt and a few green ones. If you get lucky, you can use those ones instead of raiding the ones in your locker that are nicely folded to 7x7. Aside from that, maybe some good wool socks, and that should be really all you need. It really isn't all that hard, depends a lot on the staff, but as long as you don't stress too much or take things personally (you will always get picked up for stuff on inspection and the staff are just doing their jobs) and just give'er for the 16 weeks the hard part is getting the civvie beat out of you.
The course content itself is pretty easy.
Not that you are going to need that anytime in the near future, but maybe this'll help someone starting in the nearer future.
