Once a week is the realistic minimum for a Google Business Profile to read as active - and it's a bar most local remodelers never clear. Posting consistently, even something as simple as a recent project photo with a short caption, puts you ahead of the large majority of local competitors who post rarely or never.
What to post: finished project highlights, seasonal reminders ("spring is the best time to start planning a summer kitchen remodel"), and the occasional promotion or team update. The content matters less than the consistency - profile freshness itself is a signal Google's algorithm weighs.