Yes if you want Roon to decode MQA to x2 sample rate PCM.
You don’t have as you device can decode, however, if you wish to you any DSP functionality in Roon with a MQA source the Ron must perform the MQA decoding. The is no downside to enabling MQA decoding in Roon as Roon will only use if it needs to.
Yes, otherwise the device will not be able to perform the MQA rendering.
I’d recommend experimenting and looking a Roon’s Signal Path screen… this with detail exactly what happens at each stage.