Will nec be the only problem my 4 lb baby has?

Hopefully. This is open ended question. Any thing can happen to anyone. If baby is premature, there are possibilities of complications from that.
Hard to say. When you ask a basic question with no supportive information, it is difficult to formulate an answer. The public site is not a chat room and questions are not linked. Site docs cannot see what you have uploaded or any prior questions. If you have a concern about a specific issue you are welcome to start over. Since we have no information on this particular case, we cannot provide a specific answer.