External USB Keyboard to Android (via bluetooth preferably) How to connect external USB keyboard (preferably via bluetooth) to Android device?

Best would be piece of hardware with USB socket to plug standard usb keyboard into it, that would work as "bluetooth keyboard" without need of any special software on android device.
If it's an USB keyboard, it can be directly connected to the MicroUSB port of your Android device using an OTG cable. If your device is OTG capable (most devices of the current generation are, so chances are pretty good), it should be detected automatically. That's what I do with my tablets (running Android 4.1) and a tablet-case with integrated keyboard, to transform them into a mini-notebook – it works fantastic!

As a USB keyboard usually doesn't have Bluetooth integrated, the BT approach would require some kind of adapter. I won't say there is no such thing, but at least I've never heard of any.