hello kevin,
i am just a newbie in bjj, but i would like to share my opinion about your questions; following your posts it is clear that you are more interested in the self defense application of bjj, which i am also. in my oppinion there is no need to buy the combatives dvd; why ? the gracie barra mehthod gives you a solid base for streetdefense, you will cover everything; strikes, throws, ground, self defense, etc ...
when you have a solid base, from time to time in your gym, you can train street scenarios like all out sparring against stick or knive and sparring against mulitiple oppenonts. you will discover your personnality and adapt your strategy. because in mma sparring there are no lies.
strategy is in my opinion the most important. for streetassault, just stay away out of his range§bjj strategy), if he attacks , close the distance and clinch him§bjj strategy); for many, stay on your feet and adapt, although it is difficult against many. but in my opinion it is more important to first start to survive and win against one... this is already difficult enough.
for myself i selected also a basic boxing combo starting from a natural stance; which i can use pre emptive.
that was just my opinion, find just a good gym, with a good instructor, and train, train, train, and train. there is no secret, just hard work.
kind regards
amando