I honestly think that a 2GB limit for a code base, excluding non code assets would be perfectly reasonable. If it exceeds that it should be split into separate modules.
C/C++ compilers can get huge compile time speed ups by compiling translation units as Unity files. For my work AAA game engine, a compiler can use 8GB+ per unit.
Just splitting up code might allow the compiler to use less memory, but compile time will increase hugely.
