To fix the outlines, all you'd need to do is use a single-pixel brush in pencil mode. Select the darkest color on the sprite, adjust it so that it's several shades darker, and then just trace around the sprite with the pencil tool to add the outline. If you hit a spot that's a different hue, like the metal bits on the side of the vending machine, you'll probably want to switch to a darker version of that color.
To adjust the pastel building, your simplest option is to find the "Adjust Hue/Saturation" option, then bump the saturation up by about 50%. Make sure you do this in a file/layer with JUST the building you want to change, or else you'll end up saturating all the things, and that won't fix anything. (And may cause major eye pain from stabby colors XD )