Hi @alfianaf Are you in Elastic Cloud or Self Managed.
You can scale the number of ingest nodes by deploying nodes with only ingest role only.
But more importantly that how many pipelines is how complex they are and what is throughput in terms of Events / Min etc.
The number and size of the ingest nodes will depend on that. Also unless otherwise specified your other nodes probably are ingest nodes by default, if you want to isolate ingest processing to only the dedicated ingest only nodes you will need to remove the ingest role from the other nodes.
Ingest node do not need much disk but CPU and RAM are good. Depending on your ingest needs will help understand what you needs are.
If you provide a little perspective perhaps we could suggest a starting point.
Hope this helps...