Hey HAB
Long time no speak
I have now got an ipad so have previously investigated the options...
The normal route is to connect a device that allows you to connect via XLR - either through the headphone socket ( not ideal as it goes through the ipad pre-amp) or via the lightning socket
These devices can also have MIDI sockets so you can hook up keyboards
I will dig out some links later
I am not sure about connecting via USB - I would investigate the "camera connection kit" which is the only way I know of connecting a USB device to an ipad, this might help with your "googling"
There are quite a few "app"DAW options depending on what features you want
If/when I take the plunge to record on my ipad I will be going for "Cubasis", which is based on the hugely popular Cubasis:
http://www.steinberg.net/en/products/mobile_apps/cubasis.htmlThis seems really powerful and perhaps even overkill for my needs as I would simply record to the ipad and export so I do the proper work in SONAR (my main DAW)
Good luck...