We do this job all the time. No-Nonsense Silver birch from Screwfix seems to be the preferred choice at the moment.
You have done all the prep work, so all you need to is make sure the decking is totally dry. Any moisture and you will get flaky areas later.
We use a long handle Harris decking brush. We bought in bulk years ago, so not sure if they are still available. They are basically a soft dense broom.
Pour the paint into a standard builders bucket. Dip the brush in about 1".
Work/paint each decking board about two foot. Don't be too perfectionist about the first coating. We tend to keep it thin for faster drying.
If after a few minutes you can see any pooling/wet spots, go back and rebrush it. The first coat will look a little patchy.
We recoat the same day (on warmer days). A third coat would be after 24 hours.
Depending on the decking spacing, you may need to hand brush any side runs.
Just to warn you now, i would never recommend using this product unless you are prepared to maintain and recoat indefinitely.
It does develop a film on top of the wood rather than soaking in like proper stains, so eventually wear and algae/dirt build up. Constantly wet areas will flake.
Most of our customers are wealthy and don't mind paying to have it recleaned and touched up every season. It just doesn't last like a traditional stain.
I prefer to to spray linseed oil on new decking. Even old decking can be made to look new if you gently power wash it, treat with Sodium Hypochlorite (bleach) then oil. You can even add some tints if you don't like the "new" look. Much longer lasting, no peeling/flaking and none slip.
