How to setup a Akka.NET cluster when I do not really need persistence?

I have a fairly simple Akka.NET system that tracks in-memory state, but contains only derived data. So any actor can on startup load its up-to-date state from a backend database and then start receiving messages and keep their state from there. So I can just let actors fail and restart the process whenever I want. It will rebuild itself. But... I would like to run across multiple nodes (mostly for the memory requirements) and I'd like to increase/decrease the number of nodes according to demand. Also for releasing a new version without downtime. What would be the most lightweight (in terms of Persistence) setup of clustering to achieve this? Can you run Clustering without Persistence?

This not a single question, so let me answer them one by one:

1. So I can just let actors fail and restart the process whenever I want - yes, but keep in mind, that hard reset of the process is a lot more expensive than graceful shutdown. In distributed systems if your node is going down, it's better for it to communicate that to the rest of the nodes before, than requiring them to detect the dead one - this is a part of node failure detection and can take some time (even sub minute).
2. I'd like to increase/decrease the number of nodes according to demand - this is a standard behavior of the cluster. In case of Akka.NET depending on which feature set are you going to use, you may sometimes need to specify an upper bound of the cluster size.
3. Also for releasing a new version without downtime. - most of the cluster features can be scoped to a set of particular nodes using so called roles. Each node can have it's set of roles, that can be used what services it provides and detect if other nodes have required capabilities. For that reason you can use roles for things like versioning.
4. Can you run Clustering without Persistence? - yes, and this is a default configuration (in Akka, cluster nodes don't need to use any form of persistent backend to work).