Congratulations on your pregnancy
I think the first time we bought anything for Jack was when I was about 20 weeks pregnant and we went to The Baby Show in London and bought a few bits like a play mat, a Widgey cushion (which still gets used every day), a birthing ball and DVD which I only used to sit on in labour, a breast pump and things. After that I just collected every now and then. I had a long list lol.
My Mum bought us our pram and carseat, my Dad the cot and mattress, and my future in-laws his moses basket and stand but those were all when I was around 6-7 months pregnant I think.
Clothes I never really bought much of as when I left work I got quite a lot and more than enough like vests, baby grows and bibs.
Our nursery furniture was my old but nice white chest of drawers, waredrobe and side table from when I lived at home and the white matches Jack's cot so that saved us a lot.
If you like to be organised like me then just get it all when you want! It'll fly by mostly anyway, well apart from the last few weeks for me after leaving work