We currently use a Logitech Harmony hub to control the system. Can the Dot interface with the Harmony so that Alexa can control the entire system? (E.g., "Alexa play Miles Davis" turns on the receiver and properly sets the source. "Alexa, watch TV" starts the Harmony's Watch TV activity.)
If you set it up in IFTTT, you can have the Dot trigger any of the activities that you set up for your Harmony Hub. So if you have an activity for playing Miles Davis, you can say "Echo, trigger Miles Davis" and the Harmony Hub will perform that activity. Likewise for the Watch TV activity. I have found that the triggering of activities with IFTTT usually works quite well as long as you aren't using IFTTT to trigger multiple actions in short order, but sometimes there is some lag with IFTTT - especially when you are issuing multiple IFTTT commands. Likewise, you can create IFTTT commands to turn off the devices that are used by that activity (eg, Echo, trigger turn off TV). What you cannot do is use Echo voice control to trigger simple remote button presses. So doing simple actions that don't involve turning on and off devices and setting inputs is just not there yet. So no voice activation to pause TV, play, FF, RW, change channels, change volume, etc.
We already have an Amazon Fire TV connected to our system. Do the two devices, the AFTV & the Dot, play nicely together in ways that are more than the sum of the parts?
No - they really do not integrate in any way other than having similar capabilities. The FireTV has some of the Echo/Alexa capabilities built in (everything except timers and alarms and the always listening feature), but it would have that with or without an Echo in your home. You extend Alexa's reach by having another way to talk to her and control your home automation, but it is not like the Echo/Dot will control the FireTV natively. For example, the FireTV has limited voice search capabilities, but you cannot use the Echo to trigger that functionality - you must use the voice remote.
Is there any need for an additional remote for the Dot? We already have a voice remote for the ATV[/li][/list]
If you want a remote to control the Dot, then yes. The FireTV remote will not work with the Dot. However, it will work to perform Alexa functionality via the FireTV, so if that is good enough, then no. I don't personally use a remote with any of my Alexa enabled devices except the FireTV. I would rather have a device in multiple rooms than carry around a remote - especially if I am not in the room to hear the response.