As to the other stuff, my mother was in a very similar situation. No income, no insurance, no assets, pre SS in her early 60s. But she was legally divorced.
Eventually, she took SS about a year early (age 63 or 64) and filed to claim half of her ex husband's benefit, which was larger than her own (you can choose which to claim). The SS was a bit too much to qualify for Medicaid, so she then signed up for Medicare (remember that one part (A, I think) is automatic and free, but you have to choose which version of the other part (B?) you want, and that costs some money that is taken out of the SS check).
The health insurance was SUCH a relief after 20 years without. Be warned however that dental work is not covered for the most part, and those bills are still high and out of pocket.
Normally, my mother does not need to file taxes because her SS income is so low. However, when she later inherited a bit of money, she DID have to file that year. As I noted above, she did owe some taxes on it, both federal and state, on part of that inheritance (which was, I think, a combo of insurance and regular investments). Several years later, the estate is still not completely finalized (there is a piece of real estate still to be sold) and we will have to check in again at that time, to see whether she will again need to file taxes for whatever year she finally receives the proceeds.