Sequence keys are very different from KM's hotkey philosophy. But KM is so powerful it is possible to use KM to implement sequence keys. At least I've done it. But it's very messy and very complicated, so I recommend that you don't try.
There's another problem. KM doesn't have any trigger for a modifier key tapped by itself. But KM can do polling to detect when you press the Shift key. Again, messy.
If you want to see a macro I recently uploaded that detects sequences and takes action based on a sequence, read this post. If you really want to tackle sequence key triggers, it may help to study the macro that I uploaded there.
The macro that I uploaded on that page has been running (unintentionally) on my Mac for the last week, and while my Mac has still been usable with that macro running, my keyboard has been acting a little strangely during this time. I just realize an hour ago that it was still running so I turned it off.
If you read my macro, and fully understand it, and like it, I can help you make it better to support your requirements.