Hi Witter
Haven't got time to read this whole thing so apologies if I simply repeat what others have said.
I was in a similar situation when pg with dd1. It feels hideous, and you can feel v vulnerable when pregnant. Take heart! There will be tons to go round out there.
Secondhand cheapest places I found were car boot sales and jumble sales (e.g. babygros 10p/20p). Charity shops now vary hugely in their pricing, suss out your local cheapest ones.
But free things are best. I second the recommendations for freecycle and netmums, I've had some amazing free things posted to me through netmums. I gave away our toddler bed through Freecycle. See if you've got a local secondhand baby stuff shop near you - they'll often give away less fashionable travel cots/pushchairs that have been donated.
Really, newborns need very little. A bundle of babygros, nappies, milk and a happy mum.
Agree with those on here who are giving you recommendations for crisis loans/social fund loans. Go for EVERYTHING you're entitled to, your little ones will no doubt pay tax later. Local charities can be amazing, too. I got help from a national charity for a while, I'm glad I wasn't too proud to apply. It took so much pressure off me, and made the world of difference to my DD's life.
I also endorse the comments about leaving your business on the back seat til you feel ready - there's such a thing as taking on too much.
Good luck, and congratulations!
Keep posting on here as things progress and tell us how you're doing. 