Student or Learner
1. Whoever directed this movie, it is not that good. (It is OK)
1.a. It is not that good, whoever directed this movie. (I am not sure)
2. Whoever comes to the door, tell them I am out. (It is OK)
2.a. Tell them I am out, whoever comes to the door. (I am not sure)
3- He wrote to me from Hamburg, wherever that might/could be. (It is OK)
I think sentences 1, 2, and 3 are OK but I cannot make sure if 1.a and 2.a are OK or not.