Nice design Bart!
I'm not an expert but I can give a few suggestions.

Have you considered using aluminium for the gantry in order to cut out weight? Here you have a very useful calculator to see what speed and acceleration will you have with your heavy gantry and 2Nm motors. I think that for a 150kg gantry and decent speeds you will need at least 4Nm motors and 70V drives.

Here you can find some useful information about rack and pinion. They build similar sized routers.