Is being a endodontic assistant a good job with a future?

Yes! I always recommend jobs in the dental field. The salary is usually good and most offices offer health insurance.
Could be. Many would say it is a good job, but it is not for everyone. As for a future, there won't be a lot of room to climb, but i would assume that you could cont to get raises, promotions would be limited if that is what you hope for.
Yes. There is a big difference between an experienced endo assistant and a novice. Employer will always like someone with experience. If you like endo then you should go for it.
Yes. Yes. A good assistant can put a patient at ease and make the clinical experience pleasant. This is an invaluable service in a practice where the patients almost always have some sort of concern or anxiety. A personable assistant who is also effective at assisting the dentist in making the procedure as quick and painless as possible is extremely valuable. Do it!