I've done it many times and it is a nice trip. Just note that if you are planning a trip this Sunday the steam locos are replaced by diesels due to fire hazard.
Z6 and
Z4 are scheduled on Sunday, and on Saturday the
Tp (largest Swedish narrow gauge diesel) will be used.
Faringe is a small village with a handful of houses. Although if you have some time there, you can walk over to the roundhouse and have a look at the steam locos. Apart from Uppsala, Almunge is the biggest town along the line and as mentioned where you find Augusts värdshus:
https://augustrestaurang.se . In Marielund there is a café.
If there is space, I can recommend one of there "summer coaches", without windows. (Interior:
https://commons.wikimedia.org/wiki/File:Lännakatten_sommarvagn_2015.jpg )