I made the mistake of only buying 000 for bubs - after all I was told I was having a BIG baby. Oh boy - were they wrong!!!
My DS was born a 00000 man, 000 was ridiculous!!!!
00000 lasted 3 weeks.
0000 lasted til about 7 weeks.
000 lasted up to 6 months (the smaller stuff till about 4.5 months), especially the pumkin patch bodysuits as they seemed bigger.
So, it depends on baby size! Buy a few 0000 things, most average size babies will fit this for a couple of weeks. It's nicer to have something to fit when you bring baby home and want to show bubs off. Big bubbas (4kg and over) generally can't fit smaller than 000.