Joe,
1) Acrylics only - Polly-Scale and craft store brands. I install internal bracing to prevent warping.
2) I find that basswood (clapboard siding) and paper (roof shingles) easily absorb water-based (acrylic) paints and leave no brush marks when light coats are used. They also cover well (without primer) on plastic for brick structures such as Ameritowne kits. I think my buildings might look more realistic if I used spirits-based paints but I prefer not to work with them due to flammability, vapors and cleanup.
MELGAR