The Moderna vaccine is very similar to the Pfizer vaccine (mRNA for the virus spike protein). It should have a high likelihood of success, which will increase supplies if both are available. Also, it does not require the extreme refrigeration of the Pfizer vaccine. This may open wider distribution.
Presuming no safety problems, supplies should be available early next year (January) for first responders and at risk care providers, followed by seniors and individuals with predisposing conditions and health problems. The general population should see adequate supplies by the spring (April-May). Students will be vaccinated before returning to school next fall.
While the vaccine is a true game changer, it makes staying safe in the short term really important! If you are an at-risk person with medical problems it would be a tragedy to get infected with SARS-Cov-2 when an effective vaccine is only months away.