you cant assume that you will be on the august course, but its a possibility. NETP, well, whenever there is space they may or may not throw you on, might only get part of it, I did DC school before my 3's now doing the rest of it and they split my 3's in half to let us do it. so you never know what to expect, keeps things interesting. About going home, from St. Jean you hop on a plane and head over straight away, once your here and have your in routine finished, you should be able to use some leave if you want, or save it all for Christmas, I had a month off for Christmas last year as I hadn't used any of my annual days
about twiddeling thumbs, there is definitely some of that, but they try hard to get you to a ship to do basics stuff like secure for sea, storing/de-storing, all that fun stuff, kind of boring, but you do get to play on a ship, which is better then a pat room anyday.
good luck!