Beautiful spot! Looks like a pool where a single spey with a light touch (for righties) would serve you well. To prevent commotion on the way back, lift slowly and wait until the current and rod tension lifts the line to the maximum point before sweeping the rod back into the d-loop. If you wait even a 1/2 second too long the slide will drop and the commotion will be noticeable. Too early and you'll tear it up trying to yank the line out. There's a moment of maximum lightness in the lift, get in that groove and it's not only quiet but light as a feather.
Then as you say perhaps keeping the angles to 45-60 degrees to assure a light anchor and finesse stroke with no line stick would be a good way to keep them from seeing you more than anything else. I wouldn't overhand cast, personally but that's just pers. preference.
My guess is mid-length head for the width of the pool, and I would work it without the sinktip myself until totally convinced it's necessary looking at the clarity of the water. Another option would be to have a higher rated extended belly line and fish only the forward part of the taper to keep the presentation very light and fine.
Boy I wish I could just pop into the picture and follow you through!
