No, he can’t realistically make his own social media platform in the sense of building competing one with anything other than a sliver of a chance at having any significance. Money is not the issue there.
Twitter essentially pioneered the service it provides, and became the dominant short-hand communication platform across the globe, but particularly in the west (weibo in china would be an example of a regional exception). The power of the network effect means nothing is going to realistically supplant Twitter in America absent a very unpredictable turn of events. (Those can happen, but you could be waiting 5, 10, 20 years for it, etc. - the reasonable prediction as we stand today is that Twitter remains on top for the foreseeable future.)
All major power centers (financial, cultural, political) are already on Twitter, use it to shift and mold actions and opinion, and for most topics you’re unlikely to run into censorship. Which is why people don’t leave it voluntarily almost ever - they might create an account on a second site, but Twitter is still the primary place to check for the most up-to-date discussion of most things.
For that same reason, it’s a very insidious platform, because the areas where it does engage in censorship (which it does in small increments) allow the people that run Twitter to subtly shift national discussion away from positions and opinions they disfavor. (Towards, of course, what are essentially the politics of the San Francisco bay area).
This is wrong. It’s like shutting down a public square to some disfavored people and saying, “well, they can still meet in some alleyway or something, there are free speech alternatives.” Twitter absolutely became the primary modern public square of our time. It’s kind of sad that it did, but it did. It is exercising a role and power that’s historically governmental in nature while getting away with being a company and ungoverned by the first amendment. Consumers wanting the modern public square combined with freedom of speech have no equivalent product selection, and realistically will not get one absent an intervention like Musks or some strong governmental action.
You either have Twitter, with the widest scope of reach, or you have the “free speech alternatives” with far less visibility, and therefore less relevance, to public discussion. (This is not to insult what those alternatives have built themselves, but no one thinks that Gab seriously influences national politics). A leftist, of course, is getting both benefits in full as far as they’re concerned - access to the widest network and freedom to say everything they want.
Hopefully Musk succeeds in the end, though the best outcome would be for modern legislation to classify tech companies reaching a dominant market share in certain digital services (communication, search, etc.) as something similar to public utilities and subject them to the same standards, by statute, as the first amendment does to the government. The government doesn’t have the will to do that sadly, and no one knows when or if they ever will. There isn’t (yet) an equivalent today to Teddy Roosevelt busting the trusts, but it’s far past time for legislation to be updated to deal with the tech companies, because early 20th century anti-trust laws weren’t designed to deal with it, as they were mostly focused on pricing rather than other uses of market power.
You’re confusing “free speech” with the “first amendment.” The two terms can be used interchangeably on many occasions, and sometimes people colloquially refer to free speech as “first amendment rights,” but the distinction matters if someone is trying to limit the principal of freedom of speech to the narrower use of that principal as expressed in the first amendment.
Freedom of speech is a broad principal, the first amendment is just a protection of that principal against one potentially malicious actor against it. For non-governmental actors against it, you rely on statutes to protect freedom of speech. (This is why, for instance, you have laws prohibiting employers from firing employees from discussion about work conditions or unionization - statutes protect those workers’ freedom of speech). California even has a statute to protect people from being fired for their political speech outside of work. It’s an old law, and of course today no one expects present-day California to enforce it equally, but the goal behind it was to protect freedom of speech from threats private employers might levy against certain political positions.