Google wrote the Android interface. The UI is all HTML/CSS/JS so you don't need a special app.
I'm powering it with an LFP battery and a little switcher to output 5V, both I already had sitting around, but you can use any of those phone chargers or other USB power devices. It has a micro-USB-B connector and takes 5V.
I'm probably going to offer these preassembled and tested with all the software installed. Most people don't want to have to chase down the right parts and put it together and support is more realistic if all of the hardware is known. The software is custom and you need a custom Linux build if you want it to boot fast. My dot.com entrepreneur friends are encouraging me to do a Kickstarter. Price will be comparable to other handheld recorders, under $250.