I picked up some advice for you. and hope it could help you a little bit.

The CELTA is a basic training course and you don't need to produce startlingly creative lessons. So don't waste hours trying to think up new activities or materials: Plan simple but effective lessons using/adapting published material and based on example/procedure sheets given to you by the trainers. If you spend too much time on planning, you won't have enough energy left to interact with the students when you teach your lesson! 

However hard you work, some of your lessons may go wrong. (If you could produce perfect lessons, why would you be doing the course?) If this happens, remember that mistakes are excellent learning experiences. So don't stress out or become defensive, particularly during the feedback discussions after practice lessons. With help from the trainers and your colleagues, identify what went wrong - and then make a specific effort to avoid making the same mistakes in your next lessons. 

Even if you feel stressed, be cooperative and courteous to your colleagues, your students, the trainers and the center's staff. Also, be punctual throughout the course. This is all good practice for how you will be expected to behave as a "real" teacher. Also, your behavior during the course will affect the grade that you receive and the reference that the center writes for you afterwards.

Dear Marc,

The best advice that I have for anyone about to take the CELTA (I did mine in Madrid last June) is that when they say that the course will require a lot of work during the evenings and weekends, they are NOT exaggerating or just trying to scare you.

The first week I felt a little lost, but by the second week I got on track, but I had to study, prepare my lessons or work on my projects every night and also during the weekend. The other piece of advice that I have is to NOT procrastinate on your assignments (there are four). I would starting working on two of them during the first week (I suggest the first one that is due and then choose another).

If you stay ahead of the game, you'll feel a little less stressed and that will allow you to focus better on your teaching. It will be a hard four weeks, but you won't regret it, and you'll learn things that will stay with you throughout your teaching career. I hope this helps. Good luck and best wishes. 

There's no simple answer to your question Nermine, it depends on your need or desire to develop professionally - it might help your career, it might give you satisfaction etc. But it might not. And doing courses arent they only way to continue learning - you could get a mentor who can help you do that on a relatively unofficial basis.

It really depends on if you're a native speaker or not. If you are, jobs will be coming your way - you can hop from one job to another and one  country to another. If you aren't a native speaker, good luck. This is the reality of TEFL.