I am 5'2", weigh168 lbs (currently losing more weight), and a 38DD-40DD. Am I a good candidate for Breast Reduction Surgery?

You would be a good candidate for a anchor type breast reduction.  It would be best for your to consider a reduction when you have achieved a stable weight.  Your goals seem reasonable and you should get symptomatic relief from your back, neck and shoulder pain.  

Based on your description and picture you may be a excellent candidate for breast reduction surgery at some point; you are correct in that it will be in your best interest to drop  additional weight first.
The best way to obtain insurance coverage for breast reduction surgery involves some “hoops” to jump through. The more documentation you have (for example, from your primary care doctor, physical therapist, chiropractor etc.) the better when it comes to obtaining insurance “authorization” for the procedure.
This documentation and letter/pictures from your plastic surgeon will help you obtain authorization. Make sure you are seeing a well-trained/experienced board-certified plastic surgeons.  Ask to see lots of examples of their work.
When dealing with health insurance companies, be prepared to be persistent.  In the end it will be worth it;  breast reduction surgery tends to be one of the most patient pleasing operations we perform.
 The first step would bein-person consultation with well experienced board certified plastic surgeons.  Ask to see lots of examples of their work and make sure you feel comfortable with the quality and consistency of the work performed. During these consultations, you may be able to see other patients ( similar to yourself) who have undergone breast reduction surgery.
Ultimately,  you will need to decide whether the “pros” ( benefits) of breast reduction surgery outweigh the potential “cons” ( potential risk/complications).  You may find the attached link helpful to you as you educate yourself about the pros/cons of the breast reduction procedure.
I would suggest that you communicate your goals clearly with your plastic surgeon and make sure that you have realistic expectations prior to proceeding with any type of surgery. In regards to breast size desired, also communicate carefully. In my practice the use of goal pictures are helpful in this regard; a discussion of cup size can be confusing and imprecise.   Therefore, I would not suggest that you communicate your goals and/or base your satisfaction with the outcome of surgery on achieving a specific cup size.I also find that the use of pictures is more helpful than the words “natural” or "proportionate” etc., which can mean different things to different people.Many of my patients choose to have enough breast tissue removed to help alleviate symptoms while retaining enough breast tissue to remain proportionate to the remainder of  bare torso. Again, preoperative communication will be critical.Best wishes.