Great ideas. Tear down deck , put in pavers, yes stairs leading down from sliders like old railroad ties or big stone or cement stairs. Put in a cooking area, seating area and table are.

https://www.houzz.com/photos/davisville-contemporary-landscape-toronto-phvw-vp~1975350

This just gives you an idea of a direction to go in.

I would get rid of the pea gravel and replace with a fire pit area out of pavers.

You sound like you want to get rid of the pea gravel and from a landscaping design perspective, it is not really making sense in your yard.Some people like pea gravel , some don't. You can move the pea gravel to line the perimeter of your fence/yard but honestly I think it is just too white and not necessary. Maybe some of your friends would want it? Or bag it up in manageable sizes and put at the curb with signs that say "Free Pea Gravel" - that always works where I live - LOL.

Please send more pics of the entire area and show us where you are thinking of moving the fire pit. That will help us give you better suggestions.

I'd update the white lattice, maybe strips of horizontal wood, painted the same color as the deck. Like the idea of taking off the railing- be sure to check building codes. Then do long steps, like five feet, down to a patio. Would color stained cement be cheaper then pavers?

Paint the red cellar doors too- I'd go the same color as your house to blend in

What will they be doing exactly for 25K?

Be sure to get at least 2 other estimates along with references.