The brown scum on the first two images could just be tannin from black tea. You can peel this/ the stained layers off the scoby. You can avoid it next time by not letting the tea "stew" i.e. removing the tea bag sooner (you might also need to use a water filter).
You can increase the yield with a bigger container. It needs to have a wide mouth to maximise the amount of surface exposed to air relative to the volume of liquid. I personally find my kombucha too acidic after a week so need to dilute it in a closed secondary fermentation (to fizz up) which doubles the yield.