After picking out the basic framework it was time to raise the bottom of the stairs to match up with the stringers. That process has been .. interesting! My first attempt was not high enough to end with a solid connection to the deck, and rather than lower the huge deck the answer was a higher base from which the steps would rise. I now have tall concrete blocks for the base, and the steps come to just below the patio height. The metal clip for the stringers' upper end lands solidly on the deck foundation so everything should be quite sturdy!
I didn't think beforehand about the need to level so many parts in three dimensions though! First see how off-level the deck is, then align four concrete blocks in a reasonably rectangular array, square to each other And all at the same height - or enough so that the bottom of the staps are as level as the deck itself (i.e. not quite). If that is all done properly the planks should sit on the blocks without any wobble so the stringers can rest securely on those. Once all that is done, check that the stringers reach the deck while maintaining their own level bases and top ends that are square to the deck pillars. My first iteration was too close to the deck - so down came everything so I could shift the blocks back several inches from the deck. After re-leveling, re-planking and re-measuring the result is..
It's pretty close :^)
I have a couple of spare blocks that I placed upright on the corners - whether for plants or candles remains to be seen!