Getting ready to paint the entire house.... All the books say use prime even if walls previously painted a light color. Paint store folks say don't worry about primer on light color painted walls, just prime over repairs, stains and walls not previously painted. What do you think? Where should I buy paint & what brand? Considering the local Sherwin Williams, but after reading positive comments re. Sears paints I'm wondering if I should check them out. Any good advice re. getting it right the first time greatly appreciated!