Sound like your in control Dave, clean glass, a collimation = good stargazing
Re, micro scratches, Lol, no need to worry mate, tho theyll add up if one is inclined to clean every month or two, would degrade performance in a couple of years !
As with water and detergent, doubt there be a specific ratio ? more just common sense be a good guide, an oily fry pan need a good squirt, a mirror need a couple/few drops sought of thing
Should be some tutes or even youtube demos, tho I seen one where a guy just wipes over the mirror under running tap water with a dish cloth, Lol, fair enough but that mirror wont last many years
All the best