Hey Darcy

Thanks
Layers in CC3 are called Sheets and we use them in a similar way to the way that Layers function in software like PS or GIMP.
I have approximately 135-140 sheets right at this moment in time, and add a couple more each day as I think of new things to put on the map.
Zooming and panning are relatively easy in CC3+, which is a lot faster than CC3 or any of its predecessors. Most people work with the sheet effects turned off, to increase the speed, but I have several sheets that without their transparency would be impossible to use with the effects turned off, and which I need as a visual reference. The relief shading sheets are a good example of this, since the relief shading polygons are solid black without their transparency and blur effects.
To get around having to work with the effects turned on in such a large map, I pick a level to work on (a level in the geography of the island) and work with about 30-40 sheets around that level visible, which reduces the time taken for zooming and panning to no more than about 5 seconds. I look on this time as time to think and consider my next move - to think about whether I should put this house here... or over there...or what particular shape to draw this or that patch of fill... LOL
Most CC3+ maps are about a tenth the size of this one and have only a very small fraction of the number of sheets and effects. With those there is little or no lag on zooming and panning
I hope that answers your questions
EDIT: Load time for this one? Approximately 10 seconds. Save time - negligible.