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Dave,

Instead of putting redwood on your deck, I would suggest IPA if you want to stick with wood. IPA(also known as Ironwood) is a South American hardwood. It will NEVER rot. It starts out as a brown color and turns to a dark grey eventually. However, it is the densest of all species of lumber in the world. It is even harder than Ebony. Therefore, it is extremely heavy. You also have to predrill every hole for the screws.

The other wood option is Cumaru. It is another SA hardwood that is impervious to rot. It is almost as dense as IPA. It is also available as a decking product throughout the world.

If you want to go with a composite(Trex type) I would suggest you use a capped composite decking. This is a product that has composite on the inside and a PVC wrapping around the outside.
The benefit of this product is that is does not shrink or swell in LENGTH like solid PVC. It is also cheaper than solid PVC. This is not the original composite type decking. The PVC cap has the color all the way through(about 3-4 mm).
It will not grow MOLD on the surface if you get a lot of rain in your area.

If you do not have a wide temperature swing in your area, then I would consider a solid PVC product. PVC tends to be the most expensive decking board. However, it is totally maintenance free. It will shrink in the winter. I have PVC fascia boards on my house here in NH. In January(0 degrees)there will be almost a 1/4” gap between boards on the front of my house(36’ overall length). I purposely installed these boards in mid summer when it was 80-90 degrees. I overlap the joints. That way they will shrink. IF you install PVC around here in the winter you have to allow for expansion or it will buckle.

The other benefit of composite/capped or all PVC is that they now have clips that go into a groove on the side edge of the decking. That way the decking is attached to the joists without a screw showing on the surface.
Another benefit of the composite are they can be bent around curved decks to some extent. So, you are not limited in construction to building with 90 degree angles.