Hello Lennart,
1) About porting project from keil to MCUXpresso IDE, you only can create a new project on mcuxpresso IDE, then copy&paste the code into it , compile still to there is no error.
2) About the bootloader binaries, I can try to compile on my side, then send it to you if you need, while I think it is not convenient, because maybe you need change something refer to your requirement, also debug.
BR
Alice