HN user
Get the hell away from that project asap. From a technical standpoint it's fine, and will be a lot of work.
However the lack of budget and that the management has an 'aggressive roadmap' says that the management team is toxic, ill-informed, negligent, and ignorant.
Your mental heath takes priority. Get the fuck away from that tyrefire of a company
That wasn't your failure per se. But the failure of pretty much everyone above you. That they treated you like that after the fact is pretty shitty. In hindsight I'd say that you are much better off by not being there, where you would learn bad practices.
No Stage Environment. Proactively Cancelled Backups on a Business Critical System. Arbitarily implementing features 'because they have it' rather than it having some purpose in the business model. No Test Drills of disaster scenarios. The list goes on. As I say, and you probably realise now, that you are lucky to no longer be there.