A few notes on my own personal experience, for what it's worth. I am married with 2 kids, as I was when I started IAP/BOTP.
REF: SECOND LANGUAGE TRAINING
I was one of those "in-betweens" who had some French ability when I started SLT. I was tested before I started, after indicating that I had some ability to speak French. But I fell short on the oral part (the hardest one), so I started my SLT course in January 2004. I was re-tested in May, achieved the required oral level, and left St. Jean on May 21. I started CAP on May 31, 2004. I hate to contradict the esteemed Mr. Tebo
(who is a friend of mine, BTW), but Phase training does NOT take a priority and the availability of those courses will have nothing to do with when you leave St. Jean. They may test you sooner than they otherwise might have, if there is a CAP course coming up, but ONLY if they think you have the ability to pass the test(s). At any rate, the bottom line is that you WILL NOT leave St. Jean unless you (a) achieve the required profile (BAB), or (b) finish the 33-week course (whichever comes first). I tried, believe me.
Also, family situations, unless they are EXTREME, will have no impact on how long you stay in St. Jean.
REF: MOVING TO GAGETOWN
As for the move to Gagetown, I also have a bit of experience on that topic. I was posted to Gagetown "Prohibited" in May 2004, meaning the Army would not pay for my move. I said "f*** it", and paid for it myself. Moving from Ontario, having owned a house there, it was quite a costly venture (about $20G, largely real estate fees of about $11G). Immediately after CAP (August 2004), I submitted a memo requesting that my posting status be changed, on the grounds that I was going to be in Gagetown for at least 15 months (CAP May-Aug 2004, Phase 3 Jan-Apr 2005, Phase 4 May-Sep 2005). I argued that this is not a temporary posting, and it was unreasonable to expect that I be separated from my family for that long. About a month later, my request was granted. Following that, I had to submit a request to have my moving costs reimbursed in arrears. This took quite a bit longer, as the request had to go to the Director of Compensation and Benefits Administration in Ottawa. But eventually it was approved, and I was reimbursed for pretty much everything I submitted. The only real difference was that I paid 6% of selling cost for real estate fees, and they only reimbursed me 5%, which is what they pay Royal LePage for an actual Army-arranged move (doesn't sound like a lot, but made a difference of about $1,500). So, if you're willing to go through the hassle of arranging your own move, on your own time, while you're in St. Jean, and if you can eat the cost for up to 6 months before they reimburse you, then arranging and paying for your own move to Gagetown is something you may want to consider at that time.
Hope this helps.
Murph