As it is a spring covenant having a story set around finding new books or letting them find new books along their journeys is a nice and organic way to have the players evolve. Also having the players be "responsible" for getting the new books will give them a sens of achievement and accomplishment as that would be a possible early goal they would have. Also they tend to be/get more invested in thing they do rather then things they just simply start with.
Another nice thing you could consider is using Realias, they work like Tractatus but the number of times you can study it depends on the collections quality (the quality is determined by the number of objects in the collection). They are also a good source for plot hooks. FYI Realias are a collection of things, usually of mundane origin, that can be studied for one or several purposes. I and Imreai did a post a day of ideas for them in November, https://forum.atlas-games.com/t/november-realia-a-realia-collection-a-day-for-november/11534/1, if you need ideas. =)