Chuck,
Take a look at most of the older buildings downtown. They are monochromatic, meaning one color. Go to Wally World, get some cheap spray paint, flats please, and paint the buildings one color. Look for the neutral pastel colors like tan, off white, light grey, dark red for brick (I'll get back to that later) and such.
You can put the walls together first like Doug, paint them and then install the windows. You don't have to high-light the details unless you want to. This cuts out the shakey hands part.
Then to "age" your buildings, use the old alcohol and india ink wash. Just slap it on with a fat brush and let it drip down into the "crooks and nannies" to give your building shadows and depth. It will also dirty up your windows a bit.
For the brick, use a dark red spray paint. Then, I hope you can find those craft paints, make a "wash" of diluted white craft paint and wash the brick walls with it. You want it to look like dust and color the red only in some areas. When this coat dries, do the same thing with a black wash. When it dries you should have an old looking brick wall the has red white and black blotches like the real thing. You don't have to paint individual bricks.
Here's a trick for heavily soiled industrial buildings. After you have painted your walls, seal the whole thing with Testers Dullcote. Let it dry. Then give the building a wash of the alcohol and india ink mixture. The alcohol "frosts" the Dullcote and everything looks dusty and sooty.
You can do all these steps with your hands. No steady detailed painting is involved. Actually the hardest part of the DPM kits is sanding the wall edges. Give it a try.
B-)
