It this is all for real, you've done very well. I have my doubts about the change in BF%, but that doesn't matter.
You might trim down to 12% or so, but could well find that things get difficult by 10%. This varies considerably from person to person, but someone who's been overweight is likely to find the sledding tough at low BF's.
I don't follow you here. Are you suggesting that 172 lbs is a lot of weight? It absolutely isn't. If I were you, I'd concentrate on keeping your BF within reasonable bounds and pursuing your goals for muscle/strength gain, but don't worry about the scale.
You're pretty much a newbie, so that's tough to answer. You might gain quite a bit, or might not. If muscle size is a goal for you, take a look at
http://www.hypertrophy-specific.com/hst_index.html