Little intermediate update :) Was a bit tired of engine work and as nobody responded to the calp for help with the GUI, I took a stab at it. Heres a glance at it:
Its quite amazing what a treview-widget can look like, if you tune cellrenderers and do subclassing of it. Another trick is to have multiple views on one model and reuse the GtkAdjustments, so that they scroll in sync. I used that for the first column in the above screenshot. This way the column wont scroll away and the cursor in the bigger view can't get into it :).
Now I need to do the same for the pattern view and probably tune the column-headers a bit.