Well in your case, you haven't yet applied, so its a bit different. You have months before they will even transfer then look at your file so you can do it either way as long as you send in the document soon.
But it is recommended you send everything in together. I didnt do it that way. I sent in most of my itsms then added later.
For canadianinlove, they may be asking anyday for the requested item so she doesnt really have that time to spare. Trust me its so frustrating knowing that they asked for some document and they acknowledge they received it and still wait 60 days to look at it.