As long as it's still over 50 degrees, you can stain. Just wait until it's been dry for 48 hours. I wouldn't wait until spring unless you're in a part of the country/world that's already too chilly. The stain will help protect the wood through the winter.

You have a wonderful, huge deck in a beautiful backyard. You would need to do the benches as well as the railing and steps. If it were mine, I would clean it well then put on a protective coating. That alone will enhance the color and protect it from mildew and wear and tear. You have a lot of deck to cover and if you do a stain, it will NOT be permanent. It doesn't matter which type you purchase and use, it will need to be touched up and/or restained at least every few years and that is if it is applied perfectly. If you decide to deepen or change the color later, you can do it after you've sealed it. If you darken the color with stain and decide in a few years that you wish you hadn't, stripping it all off would be a nightmare and would damage your wood. A colorful unbrella for your table, plants in pots, and some decorative throw pillows would really finish it all off. We purchase our house with a dark stained deck on it and I HATE it. It is hot and the maintenance is a killer.

Paint it the same color as the wall to make it visually disappear. Alternately, add wood paneling the same finish as the rails to the wall beneath the stairs.

First house had a kitchen with natural maple cabs. No stain. Looked great after 30 years, though they did yellow some..which is the nature of maple. Present house has bathrooms with stained maple cabs. While they’re not horrible, I did learn the hard way that maple can be very splotchy when stained.