Tony Gilroy has given insight into how the show is made.
Basically, they tape in three episode chunks. They write the show that way, they bring in one director, and shoot three episodes at once.
The plan is to do two seasons. Originally Gilroy wanted to do five seasons, one for each year of Cassian's life leading up to Rogue One, but he quickly decided after filming the first batch of episodes that it was far too big of an undertaking and decided to cap it at two seasons. Total of 24 episodes, 12 each year.