I am 49, male, disabled ,and receive $1099 per month in SSDI. I also have Medicare A, B and D(with "extra help" in paying for some very expensive prescriptions). I have a 401-k worth roughly $12,800. If I withdrew the entire amount from my 401-k it would be over the $25,000 limit. Would my Medicare be limited?? How much (roughly) would I pay in taxes on my Social Security? Alternatively, would it be an option for me not to withdraw th entire amount of my 401-k? (up to $25,000 total with my SSDI). By the way I am disabled, single , and have no dependents.

The withdrawal should have NO effect on your Medicare.

It MAY result in part of your SSDI being taxed, but the amount being taxed would be so small as to be hardly noticed.