I have asked our team to look at this question.
Thank you so much for the quick response.
Eng replied with this information:
For communities Authoring environment – Sizing guidelines are same as Sites. 
Being Write heavy and UGC heavy, publish environment should follow the recommended cloud service architecture for communities by either using ASRP ( cloud storage ) OR MSRP/DSRP ( on prem installations). Using JSRP is not a recommended deployment for production setup.
Publish Farm is a better alternative with user sync configured. UGC would be automatically sync across instances in case of SRPs ( except JSRP).
For 50-100 concurrent users .. not sure if these are actual concurrent UGC write requests or just read. But heap size of more than 16GB is least we should consider for a publish instance.
For more details on topologies refer 
For publish instance hardware sizing calculation , refer to  and use caching % almost 10 % or almost 0 for communtites use case.