Q: I see the KDevelop does not allow for usage of the delete key (or backspace deleting when text is marked).
A: go to "Options"->"Editor" and make sure that "Delete on Input" is enabled, then backspace and delete works.
Q: If I add files to my project, will they be automatically included and compiled ?
A: Yes, they are included in the Makefile.am's then and if you make a "Rebuild All" (./configure updates the Makefiles), your new added files will be included as well.
Q: If I removed a file, I get some weird linker messages. What is wrong with my project ?
A: If the removed file is a header file, that is automatically processed by automoc (running the Qt-Meta-Object-Compiler automatically on all headers), your removed header is still present as a moc-generated *.moc.cpp file and compiled. Remove the according *.moc.cpp file and rebuild the project.