1) Shipping should be soon as Ashok stated.
2) I imagine powered hubs are supported, so you could add additional dongles if desired, at this time I believe only Z wave devices are working. There is, to my knowledge, no library of bluetooth devices that are supported.
3) Yes Alexa is supported, no the echo does not act as an Echo. It means you talk to Alexa and can control via voice devices and some settings on the Almond 3, i.e. "Alexa, turn on my front lights" said to your echo will direct the Almond 3 to turn on the front lights (as you designate in the echo app).