PS: This is not a criticism but genuine curiocity why basic OS projects are so expensive given so much already out there. Also, Linus spent majority of hours each day for a year while this might be just a side gig for you.
Yeah it was a side gig for me, I did spend major of my days for the duration of 2 months last year to work on this.
In fact, I paused on the development of this project for 1-2 year.
But most of the time, it's just 1-2 hour per week side projects on average.
You pretty much have to seek out the knowledge regarding Operating systems in addition to taking on the challenge of learning something like C/C+ or Rust. You have to then break all the ways of thinking about your memory model after being given a GC language.
Understanding hardware is needed to debug specific CPU/IO issues that could be caused by assumptions or lack of knowledge.
Next comes learning the different algorithms needed by an OS in a new language and then implementing them. This takes a lot of time to get down correctly.
It's also a really small and niche community which means you don't have a lot of support from peers that understand the problems you encounter the community isn't an easy one to feel accepted into. It can be hard to get support because you need to be very detailed in your questions or you will be ignored.