Here is a quick summary of some of the important assumptions and caveats mentioned in the paper and in the FAQ section of the website, which do not get much air-time —
1 The model assumes Wuhan-like shutdown and lockdown measures for 2-3 months until early June (actually the authors use social distancing measures described in the New Zealand Government alert system Level 4, which pretty much shuts down everything).
2 The model assumes a nationwide shutdown, all states, no exceptions.
3 The plot is for the best case scenario with maximum mitigation and suppression measures in place. The range values shown in shade are not for best vs worst case scenarios, they are caused by errors and uncertainties in the model parameters.
4 To calculate the death rate, the model assumes that adequate ICUs and hospital resources will be available/created to meet demand, even though the model calculates beds and ICU shortage values.
5 The model recommends mass screening, contact tracing, and selective quarantine to be in place before we lift the mitigation measures.