OK G2 - Black Powder and its substitutes are measured in volume not weight. I figured you would know that but just to be sure.
There are several powder measures out there to get you started. I have an old one that measures from 50 - 100 grains. My friend just picked one up at cabelas that goes from 80 - 120 gr. You can buy screw on caps that replace the caps on Pyrodex and T7. Having not seen any BH209, I don't know what type of container it comes in. But if it has a narrow mouth, you may be able to pour it directly into your measurer.
Flasks are nice, and once you determine how much power your optimum charge takes, you can get different sized spouts to match your charge.
Note:for consistancy, some guys in here do take a, lets say, 80 gr by volume charge and weigh it on their reloading scale. Then the use that weight and weigh out several charges to take to the range with them in powder tubes.
As for knowing if the powder goes all the way to the bottom - its just like pellets. Once you have your powder and bullet down the bore, you should be down to your reference mark on the rod. (marked during the first loading)
As for one measuring different than the other. Probably - but this is due to grain size. For example, 80 grains of FFFg by volume will weigh more than 80 gr of FFg by volume simply because the grains are finer and there will be less air space.
Hope this helps