Re: wait or paint- winter
Personally, I would probably just wait until spring. Redwood is one of those woods which is highly rot resistant, but even pine would not rot in such a short time. Wood that can thoroughly dry out everytime it gets wet will last for year.
Redwood, like cedar, has heavy tannic acid in it. It must be primed with a primer which will prevent the tannins from making redish/yellowish stains on the finish coat. The preferred primer has traditionally been oil based, as tannins are water soluble. However, some of the new water based primers , such as Kilz Premium, claim they will stop tannin if the primer is allowed to cure for 24 hours before painting.
Primers have a short life if not covered with paint withing several weeks. If you prime now, it will be a good idea to wash the primer down before painting in the spring.
More than the general wetting of the siding, I would be more concerned that your caulking be tight against water intrusion behind ithe siding. As A stop gap meathod, you could quickly spot prime the edges to be caulk and then caulk those areas. Especially this time of year, I do not like the acrylic caulks as they will sit for a very long time before being safe from moisture. Urethane caulks are safe as soon as applied. Indeed, urethanes actually need moisture to cure, although the surfaces should be dry at the moment of application.
If you go ahead and prime and paint, many exterior house paints have good low temperature tolerance. Glidden and Behr Ultra are good down to 35 degrees. Generally, 50 degrees is the cut off point.
I your redwood is still clean from all the scraping and sanding, I see no reason to try to wash it down before painting. Just dust it down well.