How much paint for a room?
Short answer
One gallon covers about 350–400 sq ft per coat on smooth walls, 300–320 on texture. Two coats on walls and ceiling, primer on anything new or patched. Rounding up to whole gallons leaves paint for touch-ups.
This is one task. Get the whole renovation in the right order.
Enter your rooms once: every task, materials for each, what you save doing it yourself, and where you must call a pro.