Agreed with everybody-- "I expected nothing less" is how we would say it if we wanted it to be positive. Be careful, though, because in English (in the US anyway), "It's just as I expected" tends to have a negative overtone-- "Just as I expected, you left the pot on the stove and burned dinner."

Really depends on the original intent of the expression you are trying to translate. If it is some sort of idiom or 'meaning of speech' then it is pretty difficult to directly translate without knowing the equivalent in English. However, so long as the intent is correct, and it is grammatically correct, it can still get the point across. I don't see anything wrong with the statement: "You made the right decision, I didn't expect you to do anything else, because you're such a clever person," but I am not sure if that is what the original expression was meant to imply. The first statement you made sounds like "I expected nothing less." Which is a positive expression when someone accomplishes something and you are complimenting them on their abilities or achievement.

I agree with Wik, or you could also reword it "I expected nothing less (from you)"

It can be used! "I didn't expect you to do anything else", but it might be better worded as "I didn't expect anything less from you"