I'm up to episode 62 using OSX, so I'll give you my 2c from where I am:
My question is:
Is there a good way to follow along with this series on Mac OS?
Once you get to episode 26, it's all engine and the platform layer largely becomes irrelevant (I'm pretty sure it's visited later on however).
* I found this repo on GitHub which aims to use all of the same C++ code, https://github.com/itfrombit/osx_handmade is that a good idea?
itfrombit/osx_handmade is excellent - I also found it useful for pointing me in the right direction. I also tried to use the native C BSD libs wherever I could, over the Objective-C ones --- it's not going to hurt to use Objective-C, but I was no longer interested in learning it as a language so I tried to avoid it where possible. You can find my repo at https://github.com/kapsy/handmade_osx
--- it's not as polished as itfrombit/osx_handmade, but it does some things differently which might help to give another perspective.
Even with those, I would thoroughly recommend still going through the series and trying to emulate (in OSX), what is happening on the stream from the start rather than copying and pasting. It will take longer than if you were following on Windows, but you'll almost certainly learn much more than following on Windows and taking in everything verbatim.
* Should I be trying to find Xcode tutorials and learning that first?
I only use Xcode as a debugger, which isn't great (but totally adequate), and Vim for actual code editing. Even if it is your main editor, Xcode can probably be picked up just through real world usage.
* Is there some other solution that I do not know about, that I should be pursuing instead?
Or is developing on Mac OS just a terrible idea? Here be dragons, turn around now?
I would say that if you never again intend to create platform independent software that will run on OSX then it's probably not worth your time, as anything learned will just go to waste. However if you do, it's very much worth it. Initially I tried to develop HMH on Windows, first using a Virtual Machine which didn't go too well, Boot Camp (didn't work easily with 7), and then even considered buying a Windows box. In the end I decided to continue on OSX as I intended to create future projects for the platform, and it ended worth it for the knowledge gained.
Apart from the extra time spent, there really are no downsides :)