Self hosting can save a lot of money compared to Google or aws. Also, self hosting doesn’t make you vulnerable to DDOS, you can be DDOSed even without a home server.
You don’t need VLANs to keep your network secure, but you should make sure than any self hosted service isn’t unnecessarily opens up tot he internet, and make sure that all your services are up to date.
What services are you planning to run? I could help suggest a threat model and security policy.
Coops are still about the money. They’re about saving money by sharing resources with fellow workers/consumers, and maintaining democratic control over the company. You’re not going to get rich from a coop (without embezzlement), but you and your coowners will be cutting out the middle man. Obviously, it only makes sense for industries that you’re heavily invested in.