The great thing about using the past is that it gives you the most colossal freedom to invent. The research is necessary, of course, but no one writes a novel to dramatically illustrate what everybody already knows.
I don't separate my books into historical novels and the rest. To me, they're all made-up worlds, and both kinds are borne out of curiosity, some investigation into the past.
Nostalgia is something we think of as fuzzy. But it's pain. Pain concerning the past.