No, this is not a hostile takeover. A hostile takeover is if Elon bought up more than 50% of the shares. Which he can do much more cheaply than buying outright at a 38% premium.
If they decline his offer plan B may be to buy up the cheap shares until he has 51%.
Are you sure? I suspect were he actually trying to do this and had the liquidity, the price would go up as he tried to buy it.
1. There's <100 billionaires with enough wealth to buy 51% of Twitter. And even for most of them, such an investment would represent a larger share of their wealth than it will for Musk, meaning greater risk.
2. Most just aren't interested. Unlike Musk, who shows a strong affinity for the platform.