Things like the Fishing training book from Booty Bay and the First Aid book from Stromgarde (A) and Brackenwall (H) will fetch a very good price, but even the less rare items like Undermine Clam Chowder recipe (from Steamwheedle Port, Tanaris) can sell well. The Limited Supply routes in capital cities in Legion is still the same route and vendors as back in vanilla. Become a Patreon to The Gold Queen and see the limited supply routes for IF, SW, Darn, Org, UC, and TB, as well as the Booty Bay special, in videos as part of the gold guide I’m still crafting.
Only really to expand on Gráinne's comment as regards the 'collecting' and 'roster development' sections - which are, as said 'distinct' although they are intrinsically linked - I would like to point you in the direction of the in-game Achievements > Battle Pets > Collect tab. There are a series of achievements called Raiding With Leashes, pretty much all of which can be completed via the auction house - if you have the gold/inclination - or by completing old raids.