Need advice for budget accommodation, places to visit and local food to sample for 7 day tour in January for a family of 4 ages from 18 to 57.
Lots of information here about places to visit and things to do.
Sample itineraries as well.
Is it a good time to visit Japan in January?
We don't know where you want to go or what you want to see, so can't answer that question. Do some research about Japan, like those links above, and find what's interesting to you.