I just molded a base that fit the mirror gasket with smooth on epoxy. No plate required. The mirrors are heavy and I did save a few grams. More importantly I have rid the car for the mirror scoops that threw sand in my face driving the interstate with the windows down.
With your extreme weight reduction process I see no need for any cup holder, etc. Just pull it and make a plate from aluminum (thin) or lay up some carbon fiber if that is you thing. As long as you don't require the cig lighter for accessories all of it is not needed. I am a bit of a weight weenie but I will not spend money on titanium bolts for my bicycle to save a gram. I would rather ride for 50 miles and lose a few ounces.
A resealable water jug works without a cupholder. I almost always stop during a 5hr drive to do something. Actually you can tuck a bottle between the seat and frame.
That is the side molding. The rain gutter is in the back, it channels the water draining from the top under mount. The soft top also has openings just rear of the window where water flows into the funnel just like the rear gutter does. I expect the rubber side molding to be weather tight and if the rubber is sealed to the top it would not leak.