Different teams will be working on different parts. I say WILL because no one is working on them yet. I would expect them to quicken after part one since the majority of the mechanics will be in place. They want to crank them out 1 year at a time once all the teams get up and running but that's something new for SE. They've never been able to accomplish that before in the HD generation. This is why they're using Unreal 4. Basically because they will be able to use that iteration of the engine throughout this entire generation and not worry about multiple teams working on it since most everyone in the industry is familiar with Unreal.
The plan is to have all pieces out by the end of the PS4 life-cycle. VR is being heavily considered for some things. Gameplay will "evolve" as each part comes out. Right now barley anything is done. Not even all the character models have been finalized. If there's no delays it's an 8 year plan on paper. There will be delays, so it's safe to assume the complete collection (which I'm sure will have further tweaks) will be out in 10 years. If you put a gun to my head and asked me when I think part one is coming I would say fall 2018.
Realistically they can choose to "end" the parts whenever they want just to get a product out. I know the points on where they're thinking about cutting it but it's very fluid. That's why this is getting broken up, they're a public company and have to get product out the door. Hype can only last so long and a game that's been in the making for 10 years will have so many harsh criticisms that could have been fixed during the dev process. So you'll get part one, they'll take your feedback, make adjustments, part 2, make adjustments etc.
Expect same same sort of life-cycle with XV as well.
