1) Length of work experience: Is the length of candidate's work experience measured at the time of submitting the application or at the time of starting the MBA (which - on average - is 1yr after application)?

When they say that the average student has ~5 years of experience, they are looking at how much your worked prior to attending, not applying.

I mean it's often said that MBA candidates have min 2-3 yrs of work experience. Is it 2-3 yrs at the time of applying or commencing the MBA program?
commencing

2) Length of work experience 2: People from strategy consultancies or investment banks do MBA after 2-3 years of work. What would be the expected length of work experience from consumer goods industry candidates?

There is no real expected amount. It's just a matter of when you can are ready and can prove that.

3) Work experience: When it comes to applying to the US schools - is working in the tobacco industry an issue? I mean in the US tobacco business is very controversial. Would it affect my application?

It could be a delicate issue - you would have to carefully think through how you address this since eithics is top of mind for these programs.

4) Nationality: Will the fact that I'm from Eastern Europe make any difference (i.e. positive) to my application?

I believe it will help a little bit, in that this demographic is not as well represented as some others. But don't kid yourself - it's not that unusual!