You're on the right track. Not sure what to do about the strong sun as it will normally kill the chlorine pretty fast without stabilizer. However in a gunky colored pool I have no idea what will happen. I wouldn't be concerned about the TA until the conversion is done. Lowering it is pretty easy. There is a sticky at the top of the Alkalinity forum that explains how to lower it. Keep an eye on the pH though as it's at the low end and with vinyl you don't want it to go any lower. I'm a little out of my arena here so if someone else can chime in with better or corrected info I'd be grateful.
Al