The exterior siding is red cedar clapboards, which should have been painted a year or two ago. Some of the finish has worn down to bare wood, and I’m concerned about tannin bleed. My thinking is the oil stain will block the tannins, while the acrylic final coat would resist fading. There is a great deal of unprimed wood, and I’m trying to avoid priming first and then applying two coats of stain. I expect to use Cabot’s products. Thanks for your suggestions.
No, don't put any oil base stain under the acrylic paint. The paint will start peeling in just a few months. Stain is a completely different type of product and can't be used as a substitute for priming.
Use oil base wood primer, thinned slightly for better penetration. This will seal the wood and stop excessive tannin bleed. Allow the primer to dry, min. 24 hours. If any areas are showing some bleed through use Zinsser Cover Stain to seal these areas.
This will give you a good foundation for the paint and a paint job that will last.
An alternative is to use a solid color oil base stain, like Cabot's O.V.T. Solid. In this case, do the needed prep and apply 1-2 coats of the stain. Personally, priming and painting will give better longer lasting results.