It's just feels awkward to use "from" with "go," generally.

With "go," I want to use "to" or "toward." So, I'm more likely to include a destination than a starting point.

I'd more likely say, "You are leaving the house now."

Or just not mention the house, because it's probably ancient Rome, and no one had cell phones, landlines, telegraphs, etc. They're probably standing at least within shouting distance, so it's probably obvious where they are now. :)

"You are leaving now."

A very good question! It seems to be grammatically correct. But "domo" means "from home", while "a domo" means (you go) "from the house".

As far as I am aware, your translation "Now you go home." doesn't match the sentence. Since domo is the ablative case, I believe it means "out of the house". In order for it to mean "towards the house", it would be domum (the accusative case).