1. Yes. In fact, I have both versions of Insignia Voice Smart (Portable and the smaller (non-portable) versions) and prefer them over my google home (the smaller google home). They both have a clock, will show temperature (briefly on demand) and I think they both sound great. The non-portable is smaller and lighter (great for smaller spaces) and the portable is larger, has better sound (then the smaller and google home) and you can move it around the house (or take it outside and cast music from your phone).
2. No. It is basically the same as google home. You just need a wi-fi connection and a smart phone. Setup is mostly easy, but may take a few tries.
3. It uses the google home app on your smartphone. As stated earlier, it works just like a google home device.
4. It does not work with Alexa, Echo or Amazon Music. My lone disappointment thus far is that, as a Music Unlimited subscriber on Amazon, I can't listen to that on any google related device. Google home runs some of the same basic apps as Alexa (pandora, iHeartRadio, etc), but Amazon music. Maybe one day this will change, but for now, I just have both (or you can bluetooth your Amazon music from your phone).