The keyboard shouldn't be a big concern since you can get a nice Apple bluetooth keyboard that will work with the iPad 3. However keep in mind that you'll need a stand.
Or you can go for the Logitech keyboards that also acts as a stand or cover for the iPad. There are tons of keyboard solutions for iPad but imho they make it look rather bulky and not very nice, like a small laptop. This is why I went for a fairly pricey BookArc
, but that's because it sits really nicely next to the iMac. The advantage of the Apple keyboard + free stand is that you can "dock" it quickly for a music player or rss check next to your main computer, and take it off easily to read on the couch..
is another option to hold the iPad and carry the bluetooth keyboard when travelling.
There are some nice perks with using an iPad keyboard: you can play/pause, skip tracks from any music or streaming app. You can change brightness, volume. And the best shortcut is basically when you press space it wakes up instantly to the last app that was used, without going through the slide-to-unlock feature. If the last app is a RSS Reader, for example, it will usually refresh feeds at that moment.
One thing that does not work on iPad + keyboard is it does not really offer any shortcuts for application features. It has shortcuts for typing like cut, copy, past, cursor keys, and so on. I imagine it will work just fine for typing in Japanese with the non-english keyboards. However you can not switch between apps. I think Apple purposefully does not offer apps a way to take advantage of the keyboard atm, to avoid turning the iPad in a laptop... though that didn't stop third parties from making tons of keyboard cases
If you want to "alt tab" on iPad you can enable the four finger gestures in General Settings. The gesture is fairly easy to use, swiping sideways you can quickly switch.
TLDR: On the iPad at this time you can do very efficient typing, however don't expect it to work exactly like a laptop, you'll still be touching the panel to switch between apps, and even in Pages to use bold/italic/etc. This may be something to consider if Android tablets do provide this functionality.