[Yeti]

Is there a manual level check for the Adblue solution?
(kind of like a dip stick)?

I don't think there is given I believe you just screw the bottle into some sort of fitting on the tank to fill it. Don't quote me on that one though since I have not investigated it myself yet. I am just getting through my 4th tank of fuel on mine.

 

[Yeti]

So if I am to do my own refill, there is no way to know in advance how many bottles to buy since I don't know how low the fluid is...

Nope, not really.