Ah, OK.quadrant wrote:8080 because end goal is to build a simple OS for a simple CPU like the 8080/Z80.
Yes much to learn, including patience with the learning process.
I will warn you that you may find writing an OS for a 'simple' CPU is a good deal harder than for a 'more complex' one, if only due to things such as address space limits, overall performance compared to later systems, irregular instruction sets and memory models (though this also applies to x86), limited register file sizes (ditto), and a number of other factors. However, note that I said may - it will depend greatly on just what your design goals are, and perhaps on the toolchain you mean to use, so I don't want to discourage you outright.
Could you please give us a bit more of an idea of what you are looking to do, so we can give you more specific advice?