I found it requires a distributed computer system (Cluster)...
I think you've misunderstood something, although it depends a bit on how strictly you want to define your terms -- if you want to define "cluster" as a formal structure depending on specialized software above and beyond any task performed by the cluster (which is usually what is mean if you go look at stuff about "raspberry pi clusters"), this is not something required for blockchaining. "Distributed" in that sense is more along the lines of a distributed database, which is not really considered clustering -- although it does depend on specialized software, that (database) software is there for performing the specific task all nodes are participating in: Providing a distributed database.
Another formal property of clusters is that each node is essentially interchangeable and all of them are equally capable of, and arbitrarily engage in, performing the same set of tasks. Although this might apply in a restricted sense to nodes in a blockchain network, a cluster would be considered a single node in such a network, and not the network itself.
A node in a blockchain network runs independently of the other nodes in the sense that if you are the adminstrator of such a node, you do not have to have any special access to any of the other nodes -- they are run by other people. That is not how clustering works, or at least, clustering in the sense I think you will find described online with regard to the Pi.
The point is, while you could use such a cluster as a blockchain node, it is not required. You can use a single computer including a single pi (just keep in mind it won't accomplish much compared to non-educationally motivated nodes -- but then neither will a cluster of pis).
So, you have perhaps taken an interest in two distinct things, blockchaining and clustering. Do not try to pursue them together. That is a bad way to learn. Pick one or the other and focus on that.
The Raspberry Pi is probably more suitable to studying clustering, since you can buy multiples of them cheaply. For blockchaining, you might as well work on whatever normal (almost certainly much beefier and easy to use) computer you have available.