caringforpod - I would be a little bit wary of that offer. I'm not sure it's quite as great value as it makes out. For example, by my reckoning 15 Bumgenius on cheeksandcherries.co.uk would only be £4 more, and you get to choose your own colours. That's just the standard pricing when buying 15 or more by the way, not the value pack of 20. I'm not advertising their website by the way, it's just one I've shopped on in the past. The pricing on places like fill your pants is probably similar.
The reason I'd rather pay the extra £4 is that I would want to choose the colours. Personally, I would steer clear of white. I have a couple and they look grubby really fast. Particularly if they're going in the wash with those dark green ones (although, I'm actually not sure about those colours, because the V4 doesn't normally come in Ribit ,that's a Flip colour).
I'd second the recommendation of trying out a couple before you buy a full set. TBH, I'd think you might need a few more than 15 with a newborn unless you plan to tumble dry or it's really nice weather. I have about 15 for DD who is 2, and wash every couple of days. You could always buy a pack later. A lot of the standard full time packs for a newborn seem to work on 20 nappies.
I'm not personally that keen on the Flip. It can't be boosted in the same way as the v4 (or v3) can be and I find it more prone to leaks rather than less. I've only used it since DD was about one though, so it might not be an issue on a newborn. I use disposables at night, although I hope to go full cloth for DC2 (due May) and will have to do some research on what I use.
Hope that's some help. The colours are really worth thinking about. My Bumgenius are version three, so the colours were a bit different, but I wish I'd just got yellow, butternut, green and blue. They look sooo much nicer a year down the line.