Sure there is a final slipstreamed Win7, as current as whatever date it was made. It's going to come from a dubious source (arguably, if you're not familiar with where to get it), but if you get the right version for the win7 license you have, then you're not pirating it. These have been released for so long now, that any that is popular (not a new popup source) has been vetted.
There is no special risk letting a Win7 box on the internet, assuming typical things like the app itself is secure, and using a router.
However you may face a limitation in how modern the hardware can be, and have Win7 drivers.
Backing up a bit, why do you need a final slipstreamed version? If whatever you install, works for your purposes, you should be fine. If you feel like reading through the vulnerabilities list to see if any of them would impact your particular use.... have at it, but it is very unlikely. If anything, too many updates after the driver or software was produced, is more likely to break something than help.
Regardless, I'd shoot for at least a SP1 distro, then if you really want to wade through the updates list, you can find those individually, no need to apply tons of updates that don't benefit you, and just eat up some storage space. Granted, not much space in the context of running a DVR.
Lastly, there's the convenience rollup package to get there, if still available for download, but you don't need to do all the things on this link, just install win7sp1 then install the rollup:
Microsoft has finally released a "Convenience Rollup" for Windows 7 that combines updates from the past few years into one package (like a service pack).
www.howtogeek.com
support.mozilla.org
Facebook
Twitter
Instagram