“All you need” is only true at the highest level: IPFS gives you a great way to discover replicated content. It doesn't help you know that the list of known hashes is complete (consider how much work IA has spent making sure that they crawl sites completely enough to be able to replay complex JavaScript), handle the scale of that list (this is a VERY large database which updates constantly), or provide networked storage at a scale measured in the hundreds of petabytes.

Volunteer capacity at the scale of many petabytes of online storage is unproven and the long tail of accesses is enough that you're going to have to think not just about the high replication factor needed but also the bandwidth available to serve that content on a timely manner and rebuild a missing replica before another fails.