Seems that you have been through the mill to get a diagnosis as many with extremely rare diseases have. I'll answer your questions as best I can, but we are all different and TAM varies and the medical literature is often contradictory.
You asked about scorpion venom and benzodiazapines/klonopin. I can't say that these were not the cause, but TAM most commonly becomes symptomatic in middle aged males as a result of a genetic defect probably present from birth. The STIM1 gene is one that has been identified and it is likely that there are others. See "IGBMC":http://www.igbmc.fr/society/actualite/85/
Obviously your best guide as to prognosis is the past progression of your disease. Many find that over exercise hastens the progression. We all hope that it plateaus as some of the other myopathies do, but I am not aware of any evidence for this. Many who have had the disease for a long time have such difficulty walking that a wheelchair is the best way to get around. For some TAM progresses fairly slowly if they are careful. At the other extreme was one who went for 10 mile hikes, dealt with the resulting pain with hugely powerful opiodes and in 6 months could not walk across the room.
I know of only 2 deaths of people with TAM and the disease was not directly responsible. There are some with respiratory effects but I think that is rare and not fatal. The heart is the one we all worry about, but TAM almost exclusively attacks skeletal muscles. Researchers are often checking for cardiomyopathy and not finding it so it may be a miniscule possibility.
I have just reread this and it is all a bit serious. As that great man Maxwell Smart would say, "Sorry about that, Chief."