Indexing in Elasticsearch is very I/O intensive, so for best performance it is recommended to use SSDs. If you are indexing into spinning disks it is important that you spread out the indexing load across as many disks as possible, e.g. by striping them.
It is difficult to determine exactly how much data a node can index and store, so I would recommend you perform some benchmarks if you have the hardware available. I would also recommend the following resources around sizing and best practices:
https://www.elastic.co/webinars/optimizing-storage-efficiency-in-elasticsearch
https://www.elastic.co/elasticon/conf/2016/sf/quantitative-cluster-sizing
https://www.elastic.co/webinars/using-rally-to-get-your-elasticsearch-cluster-size-right