[Help with tree supports in Cura 4.6.0 that keep ending up as spaghetti monster]

The air gap is a setting in Cura called "Support Z Distance". It won't help you though because those tiny supports won't be able to handle the large structures you're trying to print on top of them. You should add the "manual supports" plugin and build a more robust support system for that area.

[Exposed gyroid infill]

I was also thinking about something similar. I'd like to print a part that would have 2-3 structural walls, filled with loose gyroid infill (10% or less). Then I would like to fill the interior with polyurethane or epoxy resin to create a PLA-reinforced resin matrix. It could save dozens of hours per part over printing with 100% infill, and would likely increase strength in the z-direction since the internal structure would end up as one homogeneous chunk of plastic instead of fused layers.

 

My current solution is also to use a drill, but that is error-prone, inconsistent and requires time that could be saved and automated if the part could be designed/printed with the ports to start.

 

For proof of concept I could go in and modify the g-code by hand to remove the walls created by the overlapping modifier, but that's not really sustainable.

 

Perhaps I could make a post-processing script if the walls created around the hole were marked in g-code? Maybe a feature in preview mode where I could select and delete individual g-code segments?