I have a babba due in March too.
I've been buying a couple of nappies a week, and have built up a pretty sizeable newborn stash now.
I've decided on mainly two parters for the newborn stage and pockets for when he's bigger. As I've bought them nearly all preloved it honestly hasn't cost that much, plus buying a couple of items a week has lessened the financial impact. Two parters just give better containment, I'm not sure I'd trust a pocket with explosive newborn poo - especially as my babies seem to have very skinny legs so I can't see many pockets (especially one size pockets) giving a good fit. I have however bought a couple of XS Fuzzi Bunz (preloved - I got two of them for 2.75 each with inserts) - for occasions when a really slim fit or ease of use is required.
You can pick up newborn fitteds really cheaply preloved and they tend to be in really good condition too as they're not used for long.
I have been buying from sites with free P&P too - like Kittykins - which I love because I can just buy one 6 quid nappy here and there when I have the money.
Also, have a look at the Nature Babies shop on ebay - they start bidding on diddy diapers at 3 quid, with 50p post and packaging. I've got several 3.50 brand new diddy diapers from there.
I guess how many teeny tiny nappies you buy depends on how big your baby is likely to be - I seem to have little babies so hopefully I should get a fair bit of use out of them. It also depends on whether super bulky nappies bother you - if you're not bothered you could just buy one size nappies which in theory sounds like the perfect solution, but something to keep in mind is that unless you buy loads and loads, with 2.5 years of continuous use they will prob be falling apart by the end.
My newborn stash consists of:
6 X Size 0 Bimbles - these are quick drying with a flap out booster, room for boosting and fleece lining. Nippa, popper or aplix.
6 X XS Sandys - great for containment
3 X Kissaluvs size 0 - cute, with a popper for the umbilical cord
1 X Size 0 Bambeasy - really absorbant and silky soft with fleece lining - Kittykins have these on offer for around a fiver
3 X Diddy Diapers - a good staple nappy, also really cheap
2 X Thirsties size 0 - these are so cute and really trim fitting especially with the Thirsties wrap
1 X Swaddlebees XS - a luxury buy!
1 X Minki Huggle XS - just in case I'm lucky enough to have a baby who sleeps for long periods from the beginning (wistful thinking)
3 X Fuzzi Bunz XS - for trim fit - they really are teeny - and when others are minding the baby
2 X Lucys Hope Chest S - another luxury, with gorgeous snap in velour boosters
3 X Thirsties XS Wraps - really small trim fitting wraps
3 X Motherease Rikki/Airflow in XS/S - a classic
1 X Blueberry Minky Wrap S - just cus they're cute!
1 X Cotton Babies wrap
Then I'll move him onto Ciaran's (pretty sizeable - enough to share anyway!) stash of pockets and night fitteds when he gets bigger.
I wouldn't worry about having lots of diff types of nappies - as long as you research each nappy you buy (have a look at the Newborn review forum which has some really handy reviews of newborn nappies). I think you need different nappies for different situations anyway. Buying 20 of one type of nappy is much more of a gamble because if you don't get on with it, you'll be stuck with 20 of them, wheras if you have a good mix of nappies that you've researched well, then it's no big deal if there's a couple you use less than the rest. After all, until the baby gets here it's impossible to know for certain whether a certain nappy will suit them or not.
When I was first starting out in cloth I very nearly bought a BTP pack of Wonderoos, and now I am *sooo* glad I didn't - it would have been an expensive mistake -because having tried a variety of nappies it turns out Wonderoos are the only ones that really don't suit Ciaran!
If you are buying trial sets, only buy them if they have nappies you actually want in them. Also, always add up the cost of buying the nappies individually and compare it to the price of the trial set - by doing this, I've found that a lot of trial sets/BTP sets actually work out significantly more expensive than if you'd bought the items seperately. Having said that, there are def bargains about.
Ok I've just realised how long I've been rambling on for, so I'll shut up now, lol. Good with with your newborn X