But, it wasn't clear to me whether the same node could be used for receiving data from logstash.
yes same node can be used as output for logstash.
In this current set-up of mine, having only 1 coordinating-only node to receive from Logstash, makes the setup have a single point of failure. Hence, would it be taxing or helping the cluster if I add another coordinating-only node?
As now you are aware of working of coordinating node . i.e. it is used for load -balancing and used for handling the search request across the cluster. in case , this node is down then we can recover via using master eligible node .
While master nodes can also behave as coordinating nodes and route search and indexing requests from clients to data nodes, it is better not to use dedicated master nodes for this purpose. It is important for the stability of the cluster that master-eligible nodes do as little work as possible.
To create a standalone master-eligible node, set:
node.master: true
node.data: false
node.ingest: false
doing this we can not face any data loss problem and also single point of failure.