Yeah Reach should easily hit 4K 60fps, all the games hit it bar Halo 2 Anniversary which doesn't quite get to native 4K due to the dual layer stuff (press 'back' button to see original graphics).
Server hosted MP is god tier and I'm one of the few people who loved Halo Reach's mp, I need a release date tho!
Also on PC the games are releasing in stages, With Reach through Halo 4 each being tweaked with user feedback until they're happy with it then onto Halo CE etc. So no Halo 2/3 mp out of the gate.
The Master Chief’s arrival on PC will happen in stages with each title releasing one by one over time - giving the development teams the ability to ensure each one is right, while giving players a chance to jump in right away, rather than having to wait for the entire suite of games to be completed. Our current plan is for this journey to begin with the launch of Halo: Reach – the fictional beginnings of Master Chief’s saga – with the rest of the titles following in chronological order thereafter. Halo: Reach, Halo: Combat Evolved, Halo 2, Halo 3, Halo 3: ODST (Campaign), and Halo 4 will each be available for individual purchase within MCC as they become available. And each game will evolve and grow over time with community input.
Hope there's cross play!