First of all, breathe... you sound overly tired.
The graywater tank is matched to the volume of the freshwater and hotwater tanks. That's so you don't try to overfill when not hooked up.
I agree, the two valve system Scamp
has for drains is a PITA. But, with the proper hoses, it's doable. Not great, but doable. There's no way any manufacturer can plan for all contingencies when it comes to hose length, and that includes a freshwater hose. You should find the sewer connector in a plastic bag under the front dinette cupboard.
Lots of folks, of all trailer brands, have mounted various containers to hold stinky slinkies. 5" plastic fence posts seem to be popular.
I, personally, don't need or want tank monitors. Over the years, I've learned to use my hearing to determine when the blackwater tank is getting full. Or I just LOOK down the hole
All this stuff falls into "Different Strokes for Different Folks." Over a few camping trips, you'll figure out what works best for you.