pglogical for OLAP queries
Yes, there's some performance impact on the master because of logical decoding. It's not usually too bad.

You can have both streaming physical replication for HA/failover and pglogical in use at the same time. However, currently if you have to fail over, pglogical can't switch to reading from the promoted replica so you'll have to re-create the subscription before you re-enable writes to the master after failover if you want to ensure consistency.