Is a WordPress developer a good career ?

Yes, WordPress is very populare more than 43%
 According to  w3techs.com , 43.3% of the world’s websites are built with WordPress. If we look at websites that are created with CMSs, that number is even higher: 65.3% of websites built with an identifiable content management system, are currently using WordPress!
  source
 It is not difficult, and you are going to have work.