I recommend buying in the second trimester but if you buy a bassinette dont buy a cot until the baby bonus arrives so you a) have room for it and b) can pay for it outright. buy your pram when you have really shopped around and make sure it can handle everything you want it to do. Make sure you can lift it to boot height or higher. aim for around 10kg. The most important thing to buy early is a car seat or hire one early on. this way you wont be stuck if you have an early arrival. aim to have it in the car at least 4 weeks early. buy it by the beginning of 3rd trimester. Other little things can be 1 or 2 items in with the grocery shopping. If you get a capsule you may only get 4 months use out of it, especially if you or your partner are tall, so it's better to get a convertible.
If I think of anything else I'll add it later