A:AnswerWorks with Harmony as long as your remote has the Smart Hub. It will not work with stand-alone remotes as it technically "talks" to the hub, not the remote. And yes, it should work with Sonos based on an announcement posted in August 2016 but I can't confirm this myself as I don't own any Sonos products.
A:AnswerYou need a preamp and passive speakers. Or if you have powered speakers, just the speakers and no preamp. The Dot can connect to a preamp via a minijack - 3.5mm cable or via bluetooth, if your Preamp has that wireless technology.
A:AnswerNo it does not they are different systems and companies which are not compatible with each other. Google Home or Chromecast Audio can cast music directly from your phone.
A:AnswerYes you can hook your bose mini speaker to the Echo Dot as long as it is a bluetooth speaker. I have hooked my Bose Minilink and also my Soundlink to the Dot.
A:AnswerThe only requirement is to link it to any Amazon account and you'll need a smart phone or tablet with bluetooth to download the Alexa app, connect to the unit, then set up the unit.
It does not do general internet searches yet though I could see that skill being added at a later date as Google's unit will do that now. If you want specific answers you can tell it to go to Wikipedia for specific topics. It will also spell words, give definitions, solve math problems and tell jokes, among other things. You can connect it to your Google calendar and ask for a list of appointments which it will read back. You can also verbally add items to a calendar, shopping list, and to-do list which Google's unit cannot. You can then ask it to read those back as well.
A:AnswerThis is a smaller version of the Echo. A full Echo is not needed for the Dot to work. The Dot just does not have the larger speaker built in, but I found the Dot speaker to be quite loud. Plus you can plug in external speakers to the Dot.
A:AnswerThe power is plugged into the wall. It needs constant power. There is no battery stock. I believe you can buy a battery base but I'm not familiar with it. The communication is wireless via wifi and Bluetooth.