How did they do it back in the day? Was basically everything from the tooling etc. just created inhouse from scratch?
They had stuff, but it was all proprietary. The N64 was a stripped-down implementation of the technology used on (high-end) SGI graphics workstations of the time. SGI certainly had all the required tools.
The Dreamcast dev kits came with CodeWarrior as an IDE iirc.
Yeah, pretty much.
They provide the devkit hardware, the specification technical documentation and the tool chain to compile the binary.
https://www.retroreversing.com/playstation-2-development-har...