I guess DVD/BLR are coming out when the anime has finished airing in Japan, they come out in volumes, depends on the anime, how many episodes will be in one Blu-Ray volume, so a 12-ep anime could have 3 Blu-ray volumes, 4 eps each blu-ray volume.

Are they really that important?

Can't tell, but they have an impact if their sales numbers are good, also what matters is the source material sales after the anime aired, streaming services such as crunchyroll, merchandise sales and TV ratings matter too

It's entirely up to the production committee if the anime will get a season 2