For a professional project I would see if I could license Forgelight 2 (that's the SOE/Daybreak engine used in PS2 and H1Z1).
Next I would look at Unreal 4 and determine the work it would take to scale to large worlds - ARK is progressing albeit with some issues.
Practically speaking Unreal 4 is way easier to "get off the ground" with than wooing Daybreak to license FL2 to a vaporware team - especially when the plan is to create a competing project.
Programmers will be the least of your problems.
(There are a lot of programmers with boring day-jobs that will be willing to moonlight on an interesting project.)
The biggest problem is core business organization and project management.
There is no demonstrated way to complete such a project *on schedule* without an operating budget.
Mods, total-conversions, get made but they are generally not completed according to the original schedule.
The next major problem is the creation and integration of high-quality artwork and sound.
For structuring such a thing I would create a bitcoin-mining-like value generation and then assign it to the people working on it.
There's some software infrastructure to create for tracking (e.g. a tray-icon tool you click to clock-in/clock-out, detect away, detect screwing around on reddit, et. al.) and just that infrastructure could be its own company.
By bitcoin-mining-like I mean I would track the time people put in and have accomplishment of milestones unleash value that is then distributed among the people that contributed time to make it happen.
That amount becomes how much of the company they own (e.g. issue private stock).