Close open Brep and divide it in quarters

Hello folks,
I am relatively new to Grasshopper and still have a lot to learn. The following object was created from a Youtube tutorial. Actually it is a model for a stadium, but I want to make a FDM-printable closed object out of it to use it as a model for a vessel or kind of planter. Therefore my questions:
How can I close the small holes in the shell, where the original design has these small pylons. I didn’t get anywhere with cap holes, boundary surfaces and patch.
I also want to close top and bottom to make it solid.
And I want to divide the body into four quarters, preferably along a seam, so that they fit on the 3D printer. But maybe that could be done on the baked surface.
I would be grateful for some tips on how to proceed. Sorry if my questions are too basic.
Hauswurz.3dm (6.8 MB) (39.6 KB)