sounds like you're on the right track with your research.
Composite will need to be cleaned with a light diluted bleach solution if there is mildew on the surface
EFC38 would be a good cleaner for your rails. Order from Deck Stains Cleaners Sealers Staining Decks Wood Decking Sealing Concrete Paver Restoration. RAD will be fine too. I would stay away from ordering straight precarbonate or stuff from the chemistry store since they will be void of the surfactants and other stuff that is in cleaners designed for wood.
Pressure washing isnt required.. but will make the job easier. Low pressure is key. Hold the gun a minimum 12 inches from the wood with a wider fan tip. If thats not available, a hose and brush will work. Let the cleaner soak for a good 10 minutes though before rinsing. You'll definitely want to use a sprayer for the cleaners. Just get a simple plastic pump up sprayer. Make sure the cleaners are mixed well so you don't have granules on the bottom that will clog the tip. If you spray at an angle and not straight onto the spindles youll get two sides at one and it will help prevent cleaner from spraying right into the back of the house. Have a hose handy and just wet the siding and plants down before and after you apply the cleaner.
If you are using EFC for the cleaner, go with the citralic for brightener. RAD system will come with both so you'll use the container they give you. If using woodtux you will want to rinse the brightener off after letting it sit for a few minutes. I believe ready seal is fine if you leave the brightener on the wood, but don't quote me on that.
Both stains will be fine for your wood. Woodtux may be a bit more difficult to apply, but if you are brushing the spindles you can control your application to prevent too much stain from building up. Brushing will be your safest bet for any stain. Or a pad applicator. If you aren't comfortable with spraying you wont want to risk getting it on everything. With brushing youll be able to see how much you are putting on the wood and brush everything over to make it even. With woodtux just keep a rag handy to go back every 20 minutes and check to make sure you dont have any shiny spots. If you do just wipe it off and go back to staining where you left off
Be careful when staining around the composite. It will be tough to get off the composite if you drip stain. Use plenty of sheets and drop clothes to cover it.