Some update of the situation:
I just finished writing a script for downloading pictures / saving locally / updating comments.
I'll check/test that more tomorrow evening.
I do the first tests on a copy of the database so you do not see anything, except errors when I make mistakes (some of you may have seen a few this evening )
It will take a while to copy all the pictures, I hope to start the real conversion on Monday, after having done tests this weekend.