Re: AmE and BrE
You can google and get a lot of this. I didn't explore this site much, but here's one: Differences between British English and American words (vocabulary)
The Southern dialects vary greatly throughout the South. Someone from deep in Cajun country in Louisiana will sound as different from someone from Raleigh, North Carolina, as they both do to someone from Chicago or Boston.
In general, the Rs are softer. North might sound more like "nawth." Some words that are one crisp syllable in Yankeeland might take two syllables. Hail: hay-ull.
Nothing, not even Dick Van Dyke's awful fake British accent in Mary Poppins, sounds worst to me than a fake Southern accent.
Watch Andie MacDowell or Matthew McConaughey or early Julie Roberts movies.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.