Hey Paul,
1. yes, yes, yes ( this is the distance your eyeball has to be to the ocular lens (eye piece) to get the full amount of light to fill the lens.
2. The 40mm means the objective lens (front lens) is 40 mili-meters in diameter, but the 50 mm is too big for the mini, it will hit the hand guard unless you get high rings. All else being equal i.e. the lens quality, magnification, tube size, and coatings, the bigger the objective lens the greater the amount of light the shooter sees. Some articles I've read say scope manufactures are playing the big numbers game. There is the law of diminishing returns. Your eye is capable of only detecting a certain amount of light, before the iris contrats, limiting the excess light to the pupil. In low light a scope can't allow more light in than there is, unless you have a starlite scope which amplifies light. I've had a 3-9x32mm bushnell, and leupold 3-9x40mm. The leupold has a larger objective, better lens coatings, and better quality lens so the leu is much brighter, and sharper than the bush. If ya get a chance to go to a gun show, or even a gun shop. Pick up some scopes and check em out. Its always better to see before ya buy. There are some good cheep scopes. Sorry if ya fell asleep during the lecture. Was probably more of the same ya already know.