Moo!
I second Lil, leave it 2 days for the hcg to double. OMGOMG I have got everything crossed so hard for you!
oh yeah, and DON'T YOU DARE LIFT ANYTHING FUCKING HEAVY IT IS SO NOT WORTH IT! Pretend you've pulled your back or something. I'm still worried that July's maybe baby didn't happen because I moved the piano...
And Lil I'm so sorry I didn't reply! Being a total dur-brain at the moment.
I'm not really the best person to ask, as after the 12 week scan I bought a few things, but once I knew there was nothing serious from the blood tests I went all out batshit.
My midwife at my booking in appt told me not to bother buying anything until 28 weeks. How could I tell her I'd already bought an entire childhood's worth of picture and reading books 3 years previously? (including a potty training book, lol).
Get catalogues from the various baby places to see what their checklists are- Mothercare has one in theirs, Boots does but never has any catalogues, John Lewis has an online one- it'll give you an idea of the basics you'll need. Me being me, as I sit here 1 day before my 20 week halfway milestone thingy, I've pretty much got everything but the kitchen sink, and a list of about 15 things still to get. I did say I would only buy essentials, but on seeing those Lamaze toys, I kind of want to buy 3 different ones for our 3 potential children, you know, on the off chance they stop making them or something [irrational shopaholic emoticon]. I've been relatively good, overdone it on the toys, and bought plenty of babygrows- in sizes 0-3, 3-6 and 6-9 months. That's really where I've been naughty. The trouble is, I like to go look in TKMaxx, and as we all know, if you don't buy it when you see it, it isn't bloody there ever again. So that's where a lot of the cost has come from. I'm keeping a track of spending in a word document, don't know if I could share that, but I've been comparing prices and buying wherever it's cheapest/ on sale/ can use a discount code.
I bought a mother & baby magazine and that was quite useful- had 2 discount codes for money off stuff which I used to buy those merino sleeping bags and totseat protable highchairs.
I would say buy clothes in 0-3 months (you don't need them any smaller, you don't know what you'll get!), and limit any toys to 0+ so they can use them straight away. Peanut will be (FX everything ok) 3 months at Christmas, so perfect timing for an onslaught of 3m+ toys. 
I used the time before I knew everything was ok to just research, research, research. Once I had a good idea of what was on the market, it meant I'm now making decisions based on ideas I've had for a while, and not impulse buys that might bite me on the bum...
I might be able to PM you my full list so far, so I don't bore anyone else to tears with it, lol.
In other news, the bedroom is (hopefully) done. After breakfast, which is going soggy while I type, I'm going to inspect the paintwork at the bottom and see if I need to do another coat. I hope not! Then I can get all the furniture back in, including the new bed. Whoop!