I would speculate that it is not enforceable. There is no provision within the 17th or within the Constitution that allows for voters to recall an elected Senator.
I believe that it varies by state.
I am not so sure. However, I do agree with you that it probably would not be enforceable. However, The Seventeenth Amendment does not affect the restriction in Article I, § 4, cl. 1, which prohibits the Congress from exercising a power to “make or alter” state regulations of elections in order to determine where Senators must be chosen.
If recall isn't specifically prohibited, one would think that it's up to state law and Lousiana's citizens to determine who represents them in the Senate.
It’s up to the individual State. New Jersey has a recall provision and a recall petition is just getting under way there.