1. DAM is better suited for visual digital assets - not sure there would be any real value in using the DAM UI for executables and images. In my opinion, DM is a better candidate for what you're planning.
2. Do you mean working with local server copies of ISOs once they are imported into Nuxeo? Or do you mean importing assets directly from the server?
3. Even if you didn't want to add custom metadata you could always use the dublincore description field to capture the version number. But, as suggested above a custom version level field makes the most sense.
4. Given the size of artifacts you will be dealing with, ingestion into Nuxeo via a server-based bulk importer is going to be a requirement. Trying to push GB+ sized files through a client browser just isn't practical. This means you will have to leverage the importer package. Not sure if you know but Nuxeo stores all binaries outside the database and metadata and indices in the database, so the solution is very scalable. As a proof of concept I suggest trying the importer with some of your bigger packages to see how it performs. If performance is a concern there are many tuning opportunities at all levels of the software and hardware stacks!

And some customers are already managing software build http://www.nuxeo.com/en/customers/electronic-arts

1) Nuxeo platform in general suit well for your need. Choosing between DM or DAM will depend of the web interface you want to expose to your users.

2) yes you can look into the Nuxeo Marketplace the nuxeo-platform-importer package addon

3) I suggest here to consider the version of third part packages as metadata and Nuxeo version more as version of the Nuxeo document representing the package. So no problem if you do so.

4) no :)

Hope this helps.