Hi Sh J,

1-  You have to sit all three exams at ONCE - in a SINGLE EXAM SITTING (CIMA earlier levels don't have this rule). Whether you would sit in one day or two days depend upon your time table. For May exams, you'll have to sit E3, P3 and F3 on the May 22nd, 23rd and on the 24th respectively. 

2- For CMGA, your course fees included access to the cimastudy online study materials. For Strategic levels, your fees does not include cimastudy.com materials. Thus, you may have to buy them seperately from cimastudy.com (my personal advise is not to buy cimastudy.com materials for Strategic levels. They're not of a very high quality!)

3- I'm sorry I could not think any of free materials for Strategic levels. You may search in Google to see what you get for free. Believe me, when I searched, I got your above question as the first result - lol :-D