Best-practice use of Resource Governor in SQL Server 2017
Supporting a hybrid workload requires more than just resource governance.  

The docs call this scenario Real-Time Operational Analytics, and it's a bunch of features all working together.

First you need row versioning to ensure that the report users don't create blocking in the database. So set the database to READ COMMITTED SNAPSHOT or force the reports to run with SNAPSHOT isolation.

With locking solved, you then need resource governance and isolation to prevent the report users from using excessive server resources.  For many workloads the OLTP part doesn't need data file physical IO, but does depend on log file IO.  So physical separation of data and log can help prevent IO from reports from interfering with OLTP.  For resource governance I would start by capping the reporting workload's CPU, IOPS, Memory, and perhaps maxdop.  

The next thing you need is to make the reporting workload less expensive.  For this use some combination of updatable nonclustered Columnstore indexes, filtered indexes, indexed views, and Columnstore compression delay.

And the final thing is that you need to use Query Store to monitor the workloads and provide visibility into the plans for the report developers.