It is pretty likely you will get two seats together. Like you said, you can probably ask somebody to move if it becomes an issue. Emeryville is a pretty busy station and it is likely some business class passengers will be de-boarding there so a few seats will likely be opening up.

I do think business class would be a little less claustrophobic than a roomette.

Yes, you will be able to eat in the nice dining car out of pocket (note that it is a big pocket, food is expensive). I do not know if business class passenger have the option to eat out of the Pacific Parlor Car (which I usually find better), I am guessing they do not.