How many IPFS pin nodes needed for consistent file availability.

I am working on setting up a pinning service for an NFT art collective project. My main question is how many IPFS nodes minimum I will need in order to make sure that each pinned file is always available? I know that sites like pinata use huge amounts of server nodes for their clients, way above my current capacity. Would 3 or 4 pin servers be enough if the needed storage is available on them? (in crypto section as it it NFT related, I know IPFS is not a blockchain)