I've done mine a few times because I actually enjoy it
Step one is sanding, I rent a belt sander for the edges, hand rails steps & smaller spots and a bigger sander for the floor. They make an awful job easier. Just make sure you buy enough sandpaper replacements so you don't have to go back to the rental place for more... nothing worse. Most places will allow you to return the ones you don't use so there is no reason to not get more than enough.
Second step is to power wash everything. The sawdust will make a mess of things and the power washer will remove it all. Then let it dry out, how long this takes depends on the weather where you live. Spring is better because the air isn't heavily and humid yet. Paint takes forever when it;s humid.
Next collect brushes appropriate for the job. A few good brushes will be worth their weight in gold. Do not think they won't make a difference, they do.
Then make sure you have the necessary solvents. Nothing is worse than spending $30 on a brush that should last you forever and discovering it wasn't cleaned properly after the last job because it's hard and brittle.
Make sure you have rags for spot cleaning. I absolutely love old cotton socks for this because they slide right over my hand for all around coverage then I just toss them in the trash.
For the rungs I am a huge fan of those big mittens covered in roller material. While they don't apply with finesse they cover well and make a tedious job go faster. I usually do 3-4 rungs at a time and follow quickly while they are still wet with a wet brush to get the brush stroke finish.
After the rungs the flat surfaces are easy and will go quickly. Here your biggest mistake would come if you don't keep the stain wet as you move through the project. You can't start the floor, stop for lunch and pick it up again. Do it all at once. I like to outline first with a great deal of attention then bring the inside in to a fast finish. Just remember to not paint yourself into a corner
Maybe there are others with better tips but this is my method and it's worked for years. Good luck!
PS- I choose my paint and stains based on whatever Consumer Reports says to do. You can sign up on-line.