I'm happy with my current setup, so I'd do the same thing again:
Mac or Windows, Desktop or Laptop?
Ubuntu desktop for me. I like having a lot of screen space, so I'd just save money by not getting a laptop. If I'm away from home, I'll just read some blogs, for which my phone suffices.
Would you use the same setup for work vs home?
Not for me, I only occasionally work from home. Also I use Windows at work.
How would you handle gaming? Would you have a separate rig for that?
I don't do gaming anymore. But if I restart someday, I'll probably do dualboot on the same machine (with the added advantage of making it hard to switch to gaming... don't want to get too addicted).
I would need a better GPU. My current PC is built for coding - the only reason it has a GPU at all is that I couldn't use two 2560x1440 screens without it.