Pre-Game Discussion
First off, that sounds amazing. If you can pull this off I think you will have a game to remember.
1). I think the ability to manage risk, within reason, might go some way towards establishing the wasteland as a "credible threat"
If you use Diamond City as the epicenter of your Commonwealth, the closest thing to a "green zone" available to the players, a relatively safe place to test, recover and rearm, then it might follow that the further you get from Diamond City, the more dangerous it becomes.
But, with that danger could come commeasured rewards. If the areas nearest to Diamond City are the most picked over, it might stand to reason that the further out you go, the better your chances of finding more valuable salvage.
If a player wants to take a big risk, and potentially earn a big reward, that's on them, and they should be aware that the chance of character death, being maimed, etc goes up. That way more risk adverse characters can progress more safely and surely, where as the risk takers can roll the dice and see where they land...
2). PVP is sticky. I would almost recommend that you forbid it without express permission from another player, especially if you make threads public.
Of course, if a player is playing something like the aforementioned concepts, those come with additional enemies, but I think those should primarily be NPC enemies, for the health of the game.
3.) I agree. What you could do is just use real world weaponry where applicable, then supplement with the more realistic energy weapons, etc. I don't think that anybody is going to feel like their immersion is broken because they find an FN-FAL or a M1 Carbine instead of whatever weird assault rifle FO4 envisioned.
A 10mm pistol can just be a large framed pistol,like in the first games, it does not need to be the size of a cinder block.
And of course the mix of tribal weapons, super mutant make shifts, raider shivs and home made pipe rifles, can all be accurately represented using rules for Low Tech, etc. Maintenance and rare ammunition could be a very big factor should you so choose.
4) I think this is going to be mostly on your end, vetting concepts and making sure they are believable, that they fit your setting, etc.
5) I like this, and it gives the characters some agency in how resources are distributed. If they find something really valuable or useful, and they are not planning using it themselves, making sure it goes to the right person, faction, player, etc can help to establish allies, favors, all sorts of things. That back and forth could add a lot of depth, rather than just "going shopping".
6.) Weather, I love it. I think a table might actually be the way to go here, rolled for day to day based on season.
I am sure there is probably a fantasy weather generator somewhere, I am sure I have used one, but things like multi day rad storms, heat waves, hurricanes, fog etc could all have dramatic effects on the whole setting. Imagine being a farmer and worrying about your crops with a huge storm blowing in. It also gives an edge to players that can plan ahead with skills like Weather Sense or Meteorology.
7.) Nice, probably worth a big disclaimer there for players expecting a video game like experience. But borrowing the setting wholesale and cranking certain aspects up or down saves a ton of work on your part. As long as people know what they are getting into, I think it could be great.