Even with mappings it is hard to tell, so your best bet is to benchmark it and see if it meets your requirements regarding query throughput and latency. If we assume your data takes up the same amount of space on disk once indexed (simplified assumption, which will depend on your data and mappings), each node will have around 630GB of data assuming 1 replica is used. This seems like a lot of data given the amount of RAM and query rate you have specified. Only a small portion of your indices will be cached, so query performance is likely to result in a lot of random disk I/O, which means you probably will need fast storage (local SSDs). I would therefore suspect you may need to add resources to the cluster.