I’d wait until after the baby shower
I'm not having a shower or announcing my pregnancy before this baby comes so I've started slowing buying things already! I bought a package of diapers or wipes every paycheck, and always check clearance sections for clothes and other baby items! I've started buying stuff for all 4 of my babies by 8 weeks. It's definitely all personal preference! I just keep everything in a bin/tote until I can start setting stuff up :)
I didn't have a shower, bought what I needed and wanted, had family wanting to buy us large ticket items and close friends that brought gifts after the baby was born. I've heard from other friends or coworkers in the past say that most of their shower gifts weren't even items from their registry which is a bummer, but not always the case.
You can get a ton of great stuff on FB marketplace or similar. Plus when some people find out you are pregnant they will want to give you all kinds of hand-me downs. So I definitely wouldn't pay full price for anything at least for a couple months.
I’m in the same boat. I’ve bought a rocking chair already but that’s because my best friend has a 6mo old who really benefits from a rocking chair so I picked it up early for when she brings kiddo over! But I’m planning on buying second hand stuff beginning ~20w but I’m hoping to get help for my big ticket items (and esp stuff I’m not getting second hand like car seats and whatnot).
With our first, we probably started closer to 25-30 weeks. I don't think there is a right or wrong answer. Definitely space things out if you are budgeting