From a very experienced FOIA litigator, most of the time your FOIA request will be denied and then you'll have to sue to get the records. Typical time for these cases is 2-4 years of court appearances in trial court, then another 2 years in appellate court to get a favorable decision.

A buddy of mine just won one that finally set the precedent that database schemas are not security:

https://twitter.com/foiachap/status/1215388081378988039

You might be able to use this website. I've always wanted to use it, but haven't come up with something "interesting enough" to submit a request for:

https://www.muckrock.com/foi/

It helps you with the process of FOIA requests, and if/when granted, hosts the responses online publicly.

Also, once you finally get the zip file of source it will be a giant mess that doesn’t have build scripts, nor documentation, etc.

So you’ll win, but won’t get want you want- a way to view, understand, improve, and share.

Or you'll find its just a mess of hundreds of off-the-shelf components glued together, none of which the government has the source code for :(

So basically you're right - you'll get an unbuildable clusterfuck.