Fencing advice

Hi all,
I'd appreciate some advice on a boundry fence im looking to build in the next few weeks.
It's a straight run of 20m between my back garden and the terrace house next door (we're the end terrace).

I've recently removed hedge and conifers that ran pretty much the entire length of the run, all stumps and the bulk of roots removed too however this obviously meant quite a bit of excavation and the ground (really decent soil it is too) is not paticularly compact in areas as a result.

I want maximum privacy, so looking to go the full 2m height and like the look of "lapped and capped" such as the picture below:





The issue I have with the above is that where I live is at quite an elevation and we get some really high winds, I need this to be STRONG. I guess the obvious choice is a hit or miss fence but then we lose the privacy unless the gaps are tiny and then it's back to the high wind problem.

So I was planning using 3m UC4 treated 4x4 fence posts and sinking them a touch over (to allow for the capping) 1m into the ground, spacing between posts 1.8m.

The rails I was going to use 3 rails of 2x4 between the posts and fit them with the Kreg HD pocket hole system ( https://www.kregtool.com/store/c13/kreg-jigsreg/p59/kreg-jigreg-hd ) for strength over toe-nailing.

I've got a set of post hole diggers (spoon type) and a long/narrow post hole spade.

I guess what I need to know really is a 3m post, sunk 1m down at 1.8m spacing over 20m run and a close board lapped design going to be bullet proof enough for some really high winds?

Finally, postcrete I'd rather avoid due to the cost (I'd need a lot of it for the depth I'm planning sinking these posts) and I hear it's not all that great anyway so I'll get a tonne of all in one ballast and cement but what's the thoughts regarding using it dry vs wet?

Or am I totally going OTT with the 3m posts and 2x4 rails with the fancy Kreg HD pocket hole screws and whatnot?

Any advice appreciated.