Second coats on similar colors are almost never recogicnized as being needed until the coat is applied and has dried. ONLY THEN WILL YOU SEE WHETHER IT NEEDS A SECOND COAT or not. Yes, painters can use a cheaper paint then what you paid for. That is solved by getting your own which, I would charge extra for because I will always have to go get more, or add second coat because home owner tried to skimp on paint, or they got the wrong color etc...
basic formula? single color exterior labor only ranges from $0.85 to $0.95 per sq foot as a BASE starting point. Prices go up depending on multiple colors, slope of surrounding areas, multiple stories..etc.Some painters charge per window to mask off. Ive seen $25 a window to $50.  Interiors without flooring can be factored the same way. When you start having to do multiple colors, cut ins, masking, room isolation...etc. the price jumps considerably. I always start with a base of $0.85 a sq foot and figure it out from there. the season plays a major role too. paint and materials are charged separatly and are typically marked up at a minimum of 15%. I always tell clients this. that way they pick the paint out they want and what quality they want as well. Anyways...thats your base. 1250 sq foot home @ .0.95 a ft = $1,187.50 (one color). Pressure washing, Add another $45-$55 per hour. a 1250 sq ft home is not going to take longer than 2-3 hours if its a single story. 
Remember: You want to get the highest quality paint your budget will allow to ensure its lasting beauty. You'll also need painting supplies like primer, brushes, rollers and painter's tape. A professional will have these items on-hand. According to statistics, paint and other supplies account for about 15 percent of a professional painter's total cost; labor will factor into 85 percent of their charges.

When coverage is difficult to estimate, add more rather than less. You can always pour the leftover back into cans. For large jobs, use the bucket and a roller screen rather than a roller tray. It’s much faster to load your roller with the screen than to use a roller pan. Simply dunk the roller into the paint bucket, then roll it along the screen until it stops dripping.
Most pros don't bother cleaning brushes and rollers if they are going to use them the next day on the same job. "Latex paint dries slowly in cold temperatures," says Maceyunas. For two-day jobs, he wraps the rollers and brushes in plastic grocery bags and sticks them in the refrigerator. "Just allow the roller to return to room temperature before reusing it," he says. Roller covers are almost impossible to clean thoroughly. Most pros buy new covers for each job.

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