Chances are on the 10th you'll go and meet your LOM for an induction, get your rule books etc. The rest of your first week will be box visits where possible, probably doing some mandatory eLearning courses, but should be fairly chilled.
For IST you'll be put up in a hotel near the training centre. Breakfast will be included and you'll have a £25 a day budget to spend on dinner and soft drinks, so keep your fingers crossed for an extensive menu or it can get really boring really quickly!
As for what to expect at IST, it's full on pretty much from day 1 so be ready to work hard both in class and on your own time in the evenings. Though IST is tough because of the sheer volume of information you have to take on board, I reckon anyone who can make it through the very onerous recruitment process can handle IST - but only if you put the work in.