In my case I kept 100GB for Windows 10 and put the other 400GB for OSX. This is a BIG TIP so make sure you make note of it, otherwise you will have issues. Windows of course being windows gave me stupid errors when I tried adjusting the partition size - but I found out it was because you have to disable the pagefile before you can adjust partition because a lot of your disk will be in use as virtual memory. You can run the OSX installer and adjust your partition during OSX install, or you can do what I did which was boot into Windows 10 and use disk utility to adjust the partition. There are lots of guides on this forum, you just have to search for them.
on the OSX partition, and Windows 10 is still there too. So far it works fine, I have final cut pro, etc. On previous builds I always used separate SSD's but this was a laptop with only one hard drive so really, I did not have much of a choice to have dual boot using one drive.
I did the exact same thing recently on my latest build. Building a CustoMac Hackintosh: Buyer's Guide
