With AirPlay will I be able to stream to iPhone, iPod Touch, and/or iTunes, or is it only to Apple TV and 3rd party speakers?
Airplay is really a technology platform that allows for streaming media on a local network. It isn't concerned with the type of device that is producing the media or consuming it.
To start with, support may be limited and may not come from Apple. However, certainly that will change with demand. For example:
Airserver allows you to stream Airplay audio and video from your iOS device to your Mac. Works great.
You can Airplay to Windows, Mac, Android, or Amazon Fire using Reflector 2. It claims to support sending rom iOS 9 devices also (but I personally haven't tested the iOS 9 support yet).
Reflector installs an app that acts as an AirPlay and Google Cast receiver. The app is available for Windows, Mac, Android, or Amazon Fire. Since Reflector supports receiving both AirPlay and Google Cast it can receive audio/video from iOS or Android.
It's from Squirrels, the same company that makes the excellent AirParrot app (which allows you send AirPlay audio and video from Windows and Mac to AirPlay and Google Cast).