hello ;
please i want somme repense for me . thank you
1-How to size ELk storage?
2-How to check storage status and detect possible saturation? Can it be integrated into an “ELK” Dashboard?
3- how can we expand the storage?
Welcome to our community! 
Benchmarking and sizing your Elasticsearch cluster for logs and metrics | Elastic Blog is a good start on this topic.
Elasticsearch has free and inbuilt monitoring that can show you resource usage - Monitoring overview | Elasticsearch Guide [8.7] | Elastic. Expansion of storage is not something Elasticsearch does, you will need to check the documentation for your OS.