Cepstrum: Good questions. I'll try for answers.
1. The way I see it, the Ferengi (for example) aren't going to range over the entirety of even the Alpha Quadrant. There's a reason, after all, that first contact wasn't made with them until TNG, in-universe. Basically, besides the UFP, I only see the Klingons and the Romulans as having both the interest and the expanse of territory needed to really be issues for first contact outside of a certain local area. Even they aren't as assiduous about it as the Feds though, because of internal issues (in the Klingon case) and their own xenophobia/isolationism (in the Romulan case). The Cardassians are poor enough that, even prior to the Dominion War, they probably were not exactly threats; The Ferengi are likely to let the Federation do the hard work of making First Contact on behalf of the galaxy, for their part, really only acting as you suggest within a very limited local area (where I'd believe that, after the Pakled, the UFP is somewhat insistent
to the Ferengi about keeping off the pre-warp folks; I just don't see a repeat of that
situation being good for anybody, y'know?). The point is that making first contact, even if you don't observe the strictures of something like the PD, takes real resources. In part, I'd imagine something like the PD actually helps limit
the resources issue - Before a certain pre-warp point, you ignore a planet except for an occasional flyby and passive monitoring, as far as Starfleet
resources go; after all, for all you know the civilizations on the planet could all be eliminated by a disease, environmental catastrophe, evolution, whatever. After a certain point, but before warp travel is achieved, you step up the monitoring. They're likely to stick around, and presuming they don't eliminate themselves through global war or the like (or something unexpected happens like an asteroid strike), eventually they'll probably get FTL travel. As that point gets closer, you increase the monitoring, trying hard for them not to notice you or suspect your presence/visiting. You also focus most of your "hands off the pre-warpers" resources here - really, doesn't require much, as by the 2380s it's likely that anybody left who doesn't have warp travel is in probably isolated areas that aren't of strategic importance. After FTL travel is achieved, PD protection goes away, and part of the reason there's a scramble on the UFP's part to make FC ASAP after that is in the (UFP-perceived) interest of the locals as much as the UFP - to negotiate something allowing the locals to not get run over by the Klingons, the Romulans, the Ferengi, unscrupulous Feddies, etc., where they assent to Starfleet providing protection, both giving them
time to wrap their heads around
the situation they just flung themselves into, and giving the UFP the grounds on which to go "Grr, no trying to take them over/fleece them blind!" to all the other powers. I wouldn't call it a protectorate status, as it's much looser than that implies, though.
2. I think Cochrane's "guy in the woods develops FTL space engine" thing seen in FC makes no sense at all
, but I do not put it as impossible or even totally unlikely that a sufficiently wealthy nation (or, more likely, alliance of nations), using national/multinational research organizations and infrastructure, could do it. I think that the closer you are to a single world government, the less motivation you would usually have to invest in a FTL space engine, because a single world government (or close to it) takes a horde of resources anyway (as does an FTL engine), and you don't have the same thing with national prestige as a motivator for funding. (Because there's a chicken-and-egg problem with for-profit anybody going for FTL...Unless you are abundantly certain you'll profit immensely from it, why would you spend nearly the massive amount of resources/money it'd take? (We'll just set the whole issue of the Ferengi aside for right now, please? They make my head hurt when I think about it.))
So, I'd say there's an even-money shot that the civilization breaking the "warp barrier" has a single world government as not.