Actually having played a ton of bball myself, the toenails being black and purplish is probably a direct result of someone stomping on your toes.
A friend of mine gets it all the time, where some big post player will step on his toes while he drives or something. His toenails usually turn all purplish, and then eventually fall off. The good news is that its mostly painless, but the bad news is that it usually takes awhile for the toenail to grow back and your toe is left unprotected during that period.
I always thought he wore shoes that were too bit too small, because I never had that problem. And it still might actually be part of the problem (tho it sounds like you need another 1/2 size or 1 size larger for your big toe to stop blistering). But recently I got stomped on by another big guy and although it wasn't too bad, part of one of my toenails did turn black and blue and fall off.
Other things you might want to look at is your gait, and whether that might affect your running. New balance's website has a good explanation of the different gaits, how to diagnose and the type of shoes you should get. It turned out that I was wearing a type of shoe that was compounding a pronation problem that I had, and as a result, I kept on randomly spraining my ankles. I got the right pairs of shoes and the problem went away (might do it for your blistering). Good pairs of shoes are really nice
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Oh.. and I'm headed to medschool next year, so all the information above is from my personal experiences from basketball, and having a readily sprained ankle. Take the advice at your own risk
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