I’ve been diving since September (23 dives so I’m just ahead of you) and I’ve collected most all my gear used. There’s a ton of old junk people think they can sell but every now and then, a reasonable item at a reasonable price is posted. If you’re time doesn’t allow shopping, it will be best to pay more and buy new.
One place I’d be careful is getting a computer. You can pay between $50 (for the right used deal) to $2000 (for a new top of the line). Since this is a vital item to your safety and enjoyment, I’d encourage you to do your homework and don’t buy someone’s old junker. I really like the Aladin Pro that I bought ($50) but I had to replace the battery (in the oil filled case by the way) and it only works for compressed air (so no nitrox possibility). Works great so I’m happy with it - for now.