My friends and I found that we had to bring materials from personal games into our coop server.
Specifically, the iron grind was too tedious with 4 people in our seed. We were only able to find 2 sunken crypts anywhere remotely near spawn because several swamps were small and had none. We finally found a few more much later. However, it was still not enough to get 4 people geared up with iron gear, let alone upgrades.