We can cut straight to the chase on the Entreprise thing.
Entreprise has a chronic problem with mis-location of the ejector block. How far off? Usually not far enough to prevent the rifle from working, except that there are often problems with the magazine follower picking up the bolt-hold-open device reliably to hold the bolt open on the last shot. To me, this is really not such a big deal. To some folks its everything.
I have two FAL's built on Entreprise receivers. The two receivers were manufactured several YEARS apart (roughly 2000 and 2004 IIRC). Both receivers have that same last-shot-hold-open issue.
A smaller percentage of Entreprise receivers have cosmetic issues worthy of complaint.
An even smaller percentage (very small) are so far out-of-spec that you need to be a very good machinist to get them to work - if it is even humanly possible to get them to work. Again, these are rare, and I would not fear Entreprise because of the unlikely chance that you will get one this bad.
Entreprise has very good warranty service - except that they won't reimiburse your shipping costs to them, and they are likely to even send you a BILL for the return shipping back to you after they repair the rifle. I never paid the bill they sent me when they repaired my STG58C many years ago. At least they DID fix the rifle (gas tube, and headspace issues).
DSA has better quality control on their receivers for sure. But, then there are things like the DSA para bolt carrier which has had people screaming about spec-issues. Nobody is perfect.
If you want to "build" a FAL yourself, be sure to take the time to enjoy the build, and don't expect to save any meaningful money. You may even end up spending a LOT more than if you had just bought a rifle ready-to-go.
There are some very nice FAL rifles that come up for sale on the FAL Files marketplace forum from time to time. That forum sees less traffic these days. But, if you keep your eyes posted for something built on a DSA or IMBEL receiver you might really make out on a good deal. Rifles built on other brands of receivers may be very good too. But there is a little more element of uncertainty with the other brands. When it comes to FAL rifles in America, show me exactly what you are looking at, and I may be able to offer some insight and guidance.