There are 3 main reasons we decided to go public:
1) The market opportunity is massive and we believe we are entering the "inside the tornado" phase where there are increasing returns to leadership. We're seeing more mainstream adoption of Amplitude as well as more companies giving a similar sounding pitch to us and we want every advantage we can have. Being public helps contribute towards that. As an example, we've gotten more press in the last 24 hours then we have in all of Amplitude's existence.
2) Having a liquid currency for our stock allows us to be much more aggressive about acquisitions and other similar moves.
3) You really should take your company public once you reach 100M in ARR. The expectation for performance across the board goes up and good companies rise to meet the moment. You're expected to do a better job of forecasting and planning your business, telling your story, sharing your long term vision, ensuring proper financial and legal oversight, and a lot else. Companies staying private so much longer has been bad for the them and for the ecosystem IMO.
We hired Morgan Stanley as our lead investment banker. As we were meeting with different banks, they were the only ones who really understood my frustration with the traditional IPO process. They also have the most expertise by far with direct listings. I was expecting a lot of resistance to my views from everyone involved in the process but talking to them was like finding a partner who I wouldn't have to constantly fight to run the public listing process "my way". Colin Stewart at MS is also probably the single most knowledgable individual on IPO/DL capital markets in the entire world.
I'll reply to some of the other questions in another comment.