From the announcement on Friday it sounded like the financial aid to companies that need it will be distributed through IRS as tax credits, or directly as cash to those companies with cash flow issues. I don't know how they aim to decide which companies qualify for the aid.
There will be several similar fiscal stimulus measures announced over the coming weeks, perhaps even bailouts.
But how much sense does it really make to have the Fed buy treasuries at a negative interest rate? They'd be paying someone else for the treasuries which they'd then have to pay interest on (instead of collecting interest), for the sole purpose of getting new money out into the economy. Obviously at that point it's time to consider alternate ways of getting the new money out there -- like just giving it out to everybody in the country as a UBI. Or if you want to do something equivalent with slightly different accounting, have Congress pass a UBI funded entirely with debt, but then the Fed monetizes the debt (and the new debt causes treasury rates to be zero instead of negative against the monetization).
Doing some kind of "targeted tax cuts" along the same lines might also work, but probably not as well, because governments suck hard at detail-oriented master plans like that and usually just end up creating a lot of harmful economic distortions. Across-the-board even distribution reduces the incentive for people to change their behavior in order to get the money while still getting the money out there, and not putting it disproportionately in the hands of the rich.
This is what happened in the 1930s. But as you say, counteracting it is as easy as printing money. Which normally has the disadvantage of causing inflation (this is what they were excessively afraid of in the 1930s), but when there are existing deflationary forces in effect, all it does is even things out.
The real question is, what happens to the money they print? Buying treasuries with it is the usual option, which isn't a total disaster (it pushes investment back into stocks by lowering the yield on bonds), but a better option right now might be paying out the new money as a UBI.
That would serve two purposes at once. One, you fight the deflationary effect, and two, you help people out whose businesses are suffering, both by giving the proprietors a UBI and by giving their customers one as well so they then have some more money to patronize businesses with. So instead of propping up stock prices artificially, you maintain their value organically by strengthening consumer demand.
This also provides a nice answer to the question, what do we do once interest rates are already zero? At that point we can use any additional new money to fund a UBI instead of driving interest rates negative.