I paint houses for a living, so perhaps my advice will be helpful.
Prep: Most important part of the process. You could spend fifty bucks a gallon for top-flight paint, but if your prep job is poor you're pissing your money away. Remove ALL loose paint, dirt, cobwebs, mildew, bird poop, etc etc. Only apply primer or paint to a clean, dry surface. Of course, you'll need to pressure wash the house before you begin scraping. Use Jomax while pressure washing- it should help with the mildew. Any remaining mildew or algae can be scrubbed by hand with a bleach/liquid laundry detergent solution. I find that more than 25% bleach has an adverse effect on plants. You'll only need an ounce or two of the detergent per gallon of solution, and be sure to rinse it completely off your siding. Patch holes with wood filler and fill in narrow cracks with siliconized latex caulk (NOT silicon caulk, which is unpaintable). Be sure to seal all the gaps around door and window trim. Rotting wood is best replaced, but Bondo will provide a temporary fix provided the board hasn't rotted through.
Vinyl siding: Ugh.
Paint: Buy the best paint you can afford. Cheap paint or stain is cheap for a reason. I'm most familiar with Sherwin Williams, but most of the major paint manufacturers make a fine product. If you are changing colors, know that two coats may be needed to provide a uniform finish. Use a quality primer as well. Cheap, fast-drying primers tend to be more brittle and hence more prone to failure. I prefer Sherwin Williams A-100, but again it's what I'm used to. If you are painting your house a dark color, have the primer tinted at the paint store.
Spray vs. brush and roll: If you've never used a sprayer before, you'll be in for an interesting time. If you're a novice, spraying your house will be more expensive and frustrating than just rolling. You'll have to mask off all your windows, doors, and anything else you don't want overspray on. You'll need to wear a respirator and eye protection. I'd recommend brush and roll. You'll get better film build (ie thickness) with rollers than with a sprayer, and make less of a mess in the process. You'll spend less money on supplies, too. Around here a professional sprayer ($900-1200 new) rents for $60.00 a day. $60.00 will buy a lot of gear for brushing and rolling. Paint out of a 5-gallon bucket rather than a tray- you wont have to refill the damn tray every five minutes.
To keep the mildew at bay, plan on pressure washing your house with Jomax or similar once a year. To preserve the wood, plan on painting again in ten years at the latest.
Congratulations on doing the work yourself. Painting isn't rocket science, but painting well requires skill and patience. If I can help you in any way, please feel free to post questions or e-mail me.
Jeremy
