2000 hours to render/encode 45 minute video, what machine should I build to make this manageable?
Before you go out and spend a lot more money on hardware, optimize your process.  Run tests on short pieces of your video, and see what you can adjust to get faster results.

For example, H.264 is pretty taxing to encode, especially at higher frame sizes.  Experiment with writing to intermediate codecs first, and then transcoding to your delivery format.  Often, that method is faster than writing directly to the delivery format.  See how long it takes your setup to churn out a five second clip directly to h.264, then time the same export to an intermediate codec + transcode.  

Another thing you can optimize is your disk caching strategy.  If your disk cache is on your system drive, try moving it to something speedy and external.  Some NLE's give you the option to use the disk cache at render time.  Experiment with these settings.  Also maybe try changing your GPU driver settings if your system allows (OSX mojave deprecates OpenCl.  Depending on your NLE/OS, Metal may be your only option).

Another small piece of advice, get a good process monitoring utility and use it to help clue you in on where bottlenecks occur.  I use XRG for Mac.  It's free, and provides more information than Activity Moitor.  If you notice that your GPU's are pegged, then think about adding GPU horsepower.  If they're not pegged, your CPU isn't either, but you notice a lot of disk activity, then think about how you might improve that.