Microsoft wouldnt sue at all.
They would not bring down a fan project which will be made available for free for everyone.
In the best scenario, they will see it like some free advertisement for one of their biggest franchise especially when Steven Spielberg annonced having read Beatties script and having discussion with MS.
As for selling weapons kits, since when they have proof?
If ever they send a Cease and Desist, first, it would simply state that the producer ends up producing and selling the object.
Which Im sure Peter can easily do.
We are not talking of a 1,000+ items for sales, and its not a production run either. As far as I know, only one guy has been sued and it for the Star Wars Franchise when maybe hundreds of armors were produced and sold from the original sculptor of the in-movie armor. Which is a violation of the accord that was made between him and LucasArts.
So if you are hired by Microsoft and you start selling off the net, then beware, but otherwise, just sell a couple for the community.
Now, dont put shadows on this beautiful project, and Pete, I cant wait to be back from my cruise to make some news on Halofr for some improvements