File size limit in 3D printing software
As a software developer and 3D printing enthousiast I can tell you that indeed, like Trish said, the limit is your memory (RAM) and loading/slicing time depends on the cpu power.
RAM: keep an eye on the memory usage in the task manager/performance/memory tab. When it reaches the top of the graph, the application will suddenly crash and disappear.
CPU: The application (cura/slicer/prusaslicer) can become &quot;not responsive&quot;. This does not always mean that the process hangs. It just means that the cpu is very busy and the program is not reporting the progress to windows. Most probably the application will recover from this if you just choose to wait.
Files do not get dumbed down when imported afaik in cura. They are shown exactly like in the STL. Don't know about other software though, but I doubt this happens.
Like you noted, this has nothing to do with Gcode, which is loaded serially.