There is no basis for that. Before Ramadhaan became mandatory, Muslims fasted, voluntarily, three days every month, not necessarily the 13th, 14th and 15th either.
Yes. In fact, a Muslim wife is not supposed to go on a voluntary fast without getting her husband's approval first. The other members gave you the evidence from the Sunna. The reason for this is simple: while fasting there is no love making.
It's not a duty; it's voluntary. If it were a duty, then the husband has no right to ask. There is no difference in this between a reverted woman and a woman who was always Muslim. Reverts do not have their own Sunna. The change of times does not change the forbidden into allowed.
The Hadeeth is what the Prophet, peace be upon him, said and did, approved and disapproved. The reason we must abide by the authentic Hadeeth is because God says in the holy Quran,
"Whoever obeys the Messenger has obeyed God." (4:80) and
"So let those beware who dissent from his order, lest tumult strike them or a painful torment. " (24:63)
What the companions wrote is called Aathaar (quotes), not Hadeeth.