My desk wobbles at full height. Anything short of replacing it?
A cross brace at the back removes most of the sway, and moving the heaviest item to the centre helps more than it should. If the wobble is front to back rather than side to side, the feet are the problem and shims fix it in five minutes.
What ratio and time for cold brew that does not taste harsh?
1:8 coffee to water by weight for a concentrate, 16 to 18 hours in the fridge, coarse grind. Harshness at that ratio is usually grind size rather than time: too fine and you over-extract even cold.
Is there a simpler version that gets most of the benefit?
Yes: do the first step, skip the automation, and revisit in a month. Most of the value is in the first step, and most of the cost is in making it repeatable before you know it is right.