Hi Robin,
As Scott mentioned, you'll definitely want to get the Apple Pro keyboard. The numeric keypad is indispensable and, while there are blue Tooth keypads out there, you won't be able to use modifiers from one Blue Tooth device to modify key clicks from another Blue Tooth device so it doesn't really work as a solution to cobble together 2 separate wireless keyboards. Go for the extended keyboard. It's worth it.
Nudging won't work unless you've selected a clip. Making a selection in the timeline is not the same as selecting a clip. If a clip is selected in its entirety, the nudge command will work. If you've made a selection, you can "capture" a clip with, if I remember correctly, Command-r (but don't quote me, it's in the Edit menu at any rate. this will create a clip from your selection which you could then nudge but the capture clip command will ask you to name the clip. It's kind of a roundabout way of doing things. Normally, I'd separate the clip at the first point with Command-e, move the insertion point or simply let the audio play until the next point, separate again with Command-e. Now you have two cuts in the waveform. If you're on the second cut, use Option-shift-tab to select back to the previous clip boundary and now you can nudge. While everything I've said thus far will get the job done, of course, there's a whole lot to consider when editing and this is just one aspect. Naturally, there are some tutorials out there that will explain things from the beginning.
Hope that helps,
Slau