If the stain is well weathered and no longer tacky or water repellant, a 100% acrylic primer with a stain sealer can be used. The final coat would be 100% acrylic exterior siding paint. This should prevent bleed-through of the tanin in redwood and be a durable finish. I used this in weather exposed areas and have had no problems. Surface preparation is minimal, but take the time to fill and sand cracks and knot holes and the final appearance will be better.

In areas where the stain is still water repellant you will need to use an oil based primer such as Zinesser Cover Stain. This is compatible with finish coats of acrylic (latex) siding paint. I use this approach under overhangs where stain is not exposed to sun or weather and it works great.

Before you apply any paint to the siding you will need to wash it to remove dirt and mildew and this can be done with a prodcut called Jomax.

Any caulking our filling will need to be done after the primer coat as caulk adhears better to the painted wood than to raw.

The finish should be an acrylic solid hide stain as it dries flatter as will look much better a regular house paint, which even though they say flat it can have some sheen which will not look good on rough siding. The solid stain will last just as long as the house paint.