Will I have to clean (or strip) and stain every year? Every 2-3 years

Do I apply the products with a sprayer? Roller? Brush?  Any tips here would be appreciated? Use a brush or staining pad

As an alternative to RAD/Defy, are there any suitable products carried by stores like Home Depot/Lowes? No, nothing decent at big box stores

I powered washed the deck but I'm not sure if it is enough.  I think I might have to strip it.  I've attached some pictures so hopefully someone can give me some direction on my first (or next step) You have to strip and brighten this. Look at RAD prep products

You might want to remove the metal fencing. Makes it hard tow rok around for prep and staining.

I live in NJ.  My deck is approx 14 x 28.  It is about 20-25 years old, in partial shade. In the past, I hired someone to power wash and seal the deck.  I think he used Thompsons Sealer but not 100% sure.  I'm thinking of expanding my DIY skills and cleaning (or stripping) and sealing the deck myself.

I've read tons of posts/reviews here and I'm leaning toward RAD or Defy.  I was also planning on using a transparent sealer.

Now to my questions.

Should i use a stain or a sealer? I'm just looking for protection not to change the color of the wood.

Will I have to clean (or strip) and stain every year?

Do I apply the products with a sprayer? Roller? Brush?  Any tips here would be appreciated?

As an alternative to RAD/Defy, are there any suitable products carried by stores like Home Depot/Lowes?

I powered washed the deck but I'm not sure if it is enough.  I think I might have to strip it.  I've attached some pictures so hopefully someone can give me some direction on my first (or next step)

Thanks in advance for your help!739,740,737,738,736,743,741,742,745,744,746,747