[magdalena]

You should go for Celta, I can't imagine native speaker with higher degree not being able to pass it. It is extremely intensive and you need to put everything else on hold while you are doing it, but it is worth it. Don't worry about your grammar - Celta is a very practical course focused on teaching methods, you will only need to revise particular grammar points for your lessons. Also, you will receive a booklet with grammatical terms before the course, as part of self-preparation pack- so really, there is nothing to worry about! Swan is great as a reference book for grammatical explanations for your lesson plans, but Murphy's "English grammar in use -intermediate" will give you more ideas what students might have problems with, so get them both :) Good luck!