Good questions, Jason.
The answers are: it depends ;-)
When in doubt, I use the standard pronunciation, not the more relaxed one.
1) For = Four
2) Today = Two-Day
3) Want To = Want To
4,5) Contractions... er, sometimes - see 6
6) Changing the copy - check with the person in charge of the project
Sometimes the end result can come off a bit stuffy depending on the copy and the character.
Fer me, it's all based on the specs fer the job, including the copy, market, characters, etc.
Hmmm... maybe there isn't a right answer!
Joe J Thomas
Joe J. Thomas Acting Portfolio