I want to inform you that I'm coming to Barcelona at the end of Spetember.
I hope to visit you one day, but at the moment I'm not sure if I will have the/enough time.
I'll phone you when i arrive."
I have added the present continuous as you suggested, and also replaced the second will with a simple present tense verb. I have also added the verb arrive in place of there.
Have the time or have enough time are both possible in this context; they both mean roughly the same thing.
I am not a teacher.
Student or Learner