Fabulous un-screwed-up I-house. I just don't see any violence done to the dignity and grace of the original, you lucky dog.
Windows original to my house were 4 over 4 (replaced with swankier 1 over 1 in the 1890s), so if that was the basic equipment for a substantial family home with no pretensions in 1864, yours might be a skosh later, like, say, 1872.
Style speculators, I note the good old Greek gable returns and wide whatsis boards.
Research on the title, if you choose to try your hand at it, will turn up lots of fascinating info, I'm sure, including useful dates.
We also are interested (very, veeeeeery interested) in the interior; we can probably help you date renovations if any.
Congratulations and welcome!