A cool little pet farm that can take minutes or ages depending on the god of luck.  This spot contains some of the most dense troll spawns in the game, and each has the highest chance to drop the parrot pet thats soo sought after.  On every serve rthis per has  amedian value of about 70,000g so picking one up can be a pretty cool feat.  Like the sprite darter hatchling spot its, a random farming spot that requires alot of RNG to pull off, but if you get it to drop you can make out in spades.  The other drops are miniscule when compared to this spot.
I'll be rating them all from 1 to 5 out of 5, in no particular order, and in 3 categories: Profitability (with a 0 also being a loss of cash due to the expensive initial cost), Usefulness and finally Flavour/Coolness/Prof Fantasy, whatever you like to call it. These are all personal opinions gathered from having a few of them myself and from what's been shared on Wowhead about ones I don't know, so feel free to share your own opinions or correct me when I am wrong, here goes:
You should equip new quest rewards when their item level starts beating out your previous set of gear. If you are currently wearing Tier 21 gear, it is best to let the quest rewards significantly beat your existing item level before using them. While a Tier bonus is worth a fair chunk of damage, the stats will quickly fall behind. Azerite gear additionally is another 1-3% per bonus, on top of raw stats.

The other addons are a great addition to the repertoire of the gold maker. Some add percentages and buying lists, while others provide price and revenue graphs to the reader. Chatter even allows you to repeat those WTS messages without sifting through pointless gossip and chatter. The in-depth workings of them will come later, as for now, more basic setup needs to be covered first.

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.