In terms of new vs not new. I tended to invest in most of it, but we are planning 3 dcs, so I wanted sturdy things to last all babies. But, you really don't need to.
I'd agree to get a new mattress (for Moses if you buy one, cot plus pram) but that's probably it tbh. The rest is up to you.
Local buy/sell sites are great (there are baby specific ones) plus obvs eBay. NCT also do nearly new sales, but I've not actually been to one so not sure how good they are.
Also, if you know people with babies they will give you loads of stuff!
I was really lucky last time as grandparents bought us a travel system, car seat, cot bed and changing table, so we were pretty much sorted with the big stuff. You're inundated with clothes when they arrive too so keep your clothing purchases to a minimum. People I didn't even know bought dd stuff! My mums friends etc