100% you can just do request response. What's nice is it can still be used to notify a user. Say they make a request that kicks off a background job, you can return UI that says the job has started, keep the connection open (cheap with v threads) and then when the job completes return the notification.

I honestly, wouldn't go down the CQRS road unless you are planning on adding multiplayer/coop/global notifications.

For the slow queries in a CQRS context I mostly solve that with caching. You can of course get fancy with datomiclike transaction queue/notification/listen fine grained pub/sub if that's your thing.