Do I need to redo this deck or it would be OK to clean it and repaint it

Painting a pressure treated wood deck is always tricky. Pressure treated wood does not seem to hold paint well, even with a good primer. Stain is usually a better alternative, but since your deck already has paint, it would have to be stripped completely before using stain.

In order for the paint to stick fairly well, the surface needs to be as clean and dry as possible. Looking at your pictures, I see a fair amount of algae in the grain of the wood. This is a very normal condition. You should however, use the pressure washer and bleach/water/TSP shrub down method to clean it up. I'd wait until April or May when temps are up in the 60's to 70's to help dry the deck and open the grain.

Select a high grip primer rather than a stain blocking type. Many manufactures have come out with new formulas that are designed to bond better. When you apply the primer, don't rush. Simply rolling on primer too quickly is not good. The primer needs to be brushed into the grain as deeply as possible. Let it dry completely. Now you can apply your deck paint as normal.

If you want to land on grass you need footings below the frost line in Iowa. Just two at the bottom.

The other option is to put in a solid stone or concrete pad. Needs to be on compacted soil with gravel under. Most importantly it needs to be level. Note that this does not officially meet code but I have never seen a deck not pass if doing this.

To clarify on what an inspector would want in a pad - it needs to run the width of your stairs, the stair bottoms should be resting firmly on pad (pad should probably extend out a few inches width wise), and pad should support a reasonable human step from the lowest step you create. I have done this in your exact situations with a variety of large stone. I think with a short stair case the only reason I wouldn't do it is if the soil is disturbed.