Low T can cause all sorts of negative symptoms. Knowing them all is not nearly as important as getting your health in better condition. For me, the only symptoms I needed to know before getting under the care of a doc for hypogonadism were low-libido, feeling tired much of the time, and brain-fog.
Greater risk for osteoporosis, cancer, and heart disease are related to low testosterone.
Thinking about "trying" a low dose of Androgel? You sound like an endocrinologist I know. :-) Don't take this as a treatment recommendation. That endo wouldn't know the proper way to do TRT if it bit him where the sun don't shine.
You asked what you could do: If you've talked with Dr. M, it may be prudent to see if either he or another TRT doc will treat you. Self-treatment for someone who has a lot of questions wouldn't be what I would suggest.