I don't think anyone knows specifically. In the main mission, you extract Paz and Chico. You can also extract a lone prisoner near the start point; he dies if you wait too long or if you get to Paz / Chico before you extract him. There are also a bunch of prisoners near Chico you can extract. One side mission gives you the option of extracting two targets instead of killing them. The ending for that mission is different if you do that, and I believe there's an achievement for doing so, too. So they probably carry over. Another side mission has a former MSF intel team member being held captive; Miller lets you know about him and he has a bunch of dialog when you're carrying him to an extraction point. There's an achievement for extracting ALL the prisoners on that op and you get a tape for extracting the intel team guy, so they probably carry over. A third side mission has 2 unique soldiers that you can extract. I don't think you get any achievements or different endings for extracting them, but the game refers to them somewhat uniquely when you extract them, so... who knows? The bonus side missions have a ton of crap in them that the game seems to track. You can erase Metal Gear game logos in Deja / Jamais Vu with a gun that has a unique flashlight, you can recreate ALL the scenes in Deja Vu, you can contract FOXDIE in Deja Vu, etc. Maybe the GAF spoiler thread or one of the streamers has posted what specifically carries over, but I haven't looked. I think it's safe to assume it will track more than your completion of the main mission, but... I don't know for sure.
This is why I like something like a 4-5 point scale with strong definitions. When you have one person's rating, you get an immediate understanding of how they felt about that game. When you take that same data point from multiple users, you can find out which Zelda / Mega Man / Metal Gear the community prefers, as opposed to going through the silly task of grading them individually on a larger scale. I suppose you could do this on a 3 category system, too, but I think you lose some granularity. It's certainly possible to get solid definitions with such a "small" scale, too. I'm not opposed to a 3 category system either, of course. As long as we don't have anything must larger than 5 points on the scale, or maybe something like a 7 item Likert, I'm good. That would be my preference, anyway, not like I'm the arbiter of anything!
Permanently. It "comes off" your sword after a certain number of hits, which is determined by the quality of the oil. But you can never run out of the oil itself. As long as Geralt has at least 1 alcohol in his inventory upon meditation, he'll replenish ALL potions, decoctions, AND bombs.
I believe some of the extracted people get carried over into Phantom Pain's Mother Base and there are rumors of people with GZ save data getting to go back to Camp Omega at some point. I don't think the exact specifics have leaked yet, or if they have, I haven't seen them.
I think it depends on whether or not we'd implement a system by which we could have users submit their own score for a game. In general I like the idea of written reviews that end with a binary or three point "rating system." It allows the writer the freedom to go off on the game for a while and ultimately the "point" is to allow someone to make a buying decision. I think there's something to be said for allowing our members rate games on something like a 4 or 5 point scale. If games get enough votes and we make the individual ratings meaningful, we'd be able to get a sense as to what the community thinks about the game more broadly. Doing a "small" scale lets the operational definitions of the scores mean something, and we don't have to quibble with nonsense like what deserves a 9.1 vs. a 9.2 since you can't have meaningful definitions on a 101 point scale. You absolutely CAN on a 4 or 5 point one though, so I'd be in favor of that. Negative World does something very similar to this and I like it a lot. I think there are different ways of going about what they do and I wouldn't want to just steal that concept from them, but when I think about community ratings for games and getting that data across the membership, I think they have a great model in place. I know a couple of their members posted here way back in the day, but I'm not sure if they're still involved with Negative World generally, and I haven't seen them here in ages.