A lot of the questions are very open ended, but here are some thoughts on a few of them.
One way would be to make content that others find worthy of voluntarily pinning or viewing through IPFS and caching.
No. There are other benefits to decentralized storage besides having other nodes store your files for free. Here's a blog post with some thoughts related to your statement/question.
ipfs-cluster is for nodes you control, so it gives you guaranteed replication across nodes. It doesn't matter what nodes that you don't control do (or say they do). Malicious nodes could hypothetically say they have a file when they really don't.
What do you mean by "low latency"? Latency of what operation?
Latency of file retrievals is dependent upon a variety of factors like network latency between nodes, how many nodes have the content you're requesting, how many of those peers you're connected to, etc.