I can't answer the detailed financial questions you ask. My husband handles a lot of that. What I can say is that I was, personally, not able to receive/keep pay from the private long-term disability through my old employer for months I received SSDI. I was terminated from my old job before receiving SSDI, though my private long-term disability continued for a while. The private long-term disability did have an end date (because it was disability for mental illness), which luckily was after I received my first SSDI payments. But as I said, I couldn't receive both SSDI and private disability for the same months. In the end, I had to pay back the private disability insurance company for the months I received SSDI for. That was kind of rough because my private long-term disability monthly payments were higher than my SSDI payments. Boo hiss!

To my knowledge I do pay taxes on my SSDI, but not that much. I do not, personally, have any additional source of income.