Glaswegians pronounce the following sentence as any BBC newsreader might.
"Seven sore seats at a party".
Whereas... me and my Buddies pronounced it, "Seevin sair sates et a pairty".
And as for "so" at the start of a sentence....
It's er…. like.... well... the old reason - to give the user time to think what they're gaunie say.
Or, if you listen to politicos using it in an interview, it's to ignore the question being put to them, then to continue their previous line of answering or to veer in a different direction from that intended by the interviewer.
Good interviewers understand that, see it as weakness now and it's good to see them keep pressing with the same question, which often then does get an answer, as it can't be avoided.
IMHO