I used objects to manage the panels and I'm just using the namespaces for each tabs script, with each script stored in a separate file. I'm going to experiment with placing the functions into variables to see if it makes it a little easier to manage, although so far it hasn't been too complex.
There is actually a skin/wallpaper image there that hasn't come out at all in the low res GIF unfortunately. The drop down menu image is actually part of that background image, as is the heading text for each section of controls.
I designed everything in Inkscape, the knobs and sliders were rendered in KnobMan. The dynamic text for things like knob values, the articulation names, and the CC names are all rendered directly in HISE using fonts.
If we could render sliders directly that would be awesome, I haven't spent any time with the drawing functions in HISE but now you've mentioned this I think I'll have to go down that rabbit hole too. :)