So far it looks like you won't need Gold to play online for the PC version as well as 'supposedly' if you own the digital version of the Xbone MCC you'll have those games for the PC Version too.
looks like they are releasing it in phases
Reach first, so bring on the waterworks for the most depressing Halo game first.
I do own the MCC, a college friend and I are at Halo 4 on our Legendary Co-op playthrough (we mainly play in the summer time). Which means we have H1A, H2A, Halo 3, and Halo ODST completed on Legendary.
Yep, they want to release it for PC in Chronological order rather then release order for all the fans who never played on the console and can experience the story from 'start to finish.'
Honestly means my Xbone is going to be used less and less now as the main reasons I had it was for Halo franchise and Gears and now both of those have jumped to PC as well...