I agree with one part of what you're saying: the bare Necessary Being Argument establishes a necessary foundation, but it doesn't simply define that foundation as "God." So the question becomes what kind of necessary reality could actually serve as the ultimate explanation.
But that's where your alternatives have problems.
A brute law isn't an explanation of why contingent reality exists. A law describes how things behave; it doesn't obviously explain why there is a reality for the law to govern.
An abstract object has a similar problem. Numbers, propositions, or logical truths may be necessary in some philosophical accounts, but they don't appear to have causal power. The question isn't merely "what necessary thing exists?" It's "what necessary reality can actually ground the existence of contingent reality?"
And a multiverse doesn't automatically solve the problem either. If the multiverse could have failed to exist or could have been different, then it's contingent and the original question simply remains. If you say the multiverse itself is necessary, you've accepted the existence of a necessary foundation; now you have to independently establish why a necessary multiverse is a better explanation than a necessary cause.
And there's another important point: I'm not claiming that "necessary = personal" by definition. I'm arguing that we need another premise to get there.
For example:
P1. A necessary foundation cannot be a contingent physical object.
P2. Abstract objects are causally inert; they don't cause concrete things to exist.
P3. A law describes regularities but does not itself produce the concrete reality governed by it.
P4. Therefore, an abstract principle or law cannot by itself be the sufficient cause of contingent concrete reality.
P5. If the universe has a beginning, its sufficient cause cannot simply be an eternally operating impersonal mechanism whose sufficient conditions have always been present, because then the effect would also be eternally present.
P6. A timeless necessary cause can produce a temporal effect if the cause has the capacity to initiate the effect rather than being mechanically compelled by prior conditions.
C. Therefore, a personal/agent-like necessary cause is a serious philosophical conclusion from the argument, rather than something I merely renamed "God."
You can reject P5 or P6, but that's where the actual debate is.
So yes: the first argument gets us to a necessary foundation. The additional premises are what argue that the foundation is not merely an abstract fact or impersonal law, but an agent capable of grounding a contingent universe.