Claiming no expertise here, but I overwintered some Angelonia one year in the basement. I was far from scientific about it. I dug the root balls out of the containers, trimmed the stems back (maybe to 5", not positive) and shoe-horned them all into one pot. The basement is cool but far from freezing and there was some light from a window but not "sunny." I watered them lightly about once a month, just enough to keep them alive. They basically sat there all winter semi-dormant and looking no different. In spring, I threw them back outside and they started growing again. They had experienced some really cold, near freezing temps before I brought them inside in the fall so that may have put them in a semi-dormant state. After all, it freezes in Zone 9 so the Angelonia plants must go dormant there like any other herbaceous perennial. I seem to recall that they had plump, white roots that made it easy to see that they were still alive.
Unless tender plants are really tropical, I find it much easier to store them cool and dormant or semi-dormant. Otherwise, pests become a nightmare.
You can also collect seeds from them, in addition to cuttings.
