Hi Isabelle, I guess it varies with different dialect groups and religion. For example, some say ROM considered so you don't have to do the whole wedding first, some say traditional then recognise.
Guess if you wanna get married quickly in the eyes of law, you'll need to visit the ROM website and get a date first. And for the date selection, depends on whether you're gonna get a geomancer or go temple and enquire.
Maybe you wanna ask around people with the same dialect & religion as you first?