Hi childondaway, congrats on your pregnancy With both my pregnancys i started buying things from about 12 weeks. I found it better to buy things gradually so that i didn't get to my third trimester and have to buy everything in one go. I'm a huge advocate for vinnies/ebay shopping when it comes to bubs, i have bought all DS1's clothing from birth till now (2 1/2 years) from vinnies (except for some essentials, singlets, shoes etc) and i'm now using the same clothes for DS2. They're all still in good condition and you wouldn't know they're second hand, alot of them are name brands like pumpkin patch, papoose etc and i only spent a few bucks on each item! Seriously i reckon its the best (and most cost effective) way of buying bubs stuff. I've even bought toys and bedding second hand and saved heaps.
If you don't feel comfy with going into opp shops ebay has tons of bub stuff, you can pick up second hand bulk bub clothing so cheaply. Saves a lot of $ and time walking around the shops.
HTH