I can not give you exact answer but last year I did it there.. what i noticed was , they wanted dubble copy of everything and needed wittness for interview just to have chat and make sure I and my wife are really marraid. All in all they were nice an I had no problem.
This year it will be CW for me as I have moved to new place.
I did few days ago in Cheang Wattana and police clearance was not asked at all.
However, different offices has different requirement! Last year I did in Nonthaburi office and they asked for wittnes to verify our relationship! They interviewed the witness for an hour...