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.
Good question. Me personally, when I use a new strat from somebody else, I always read thru the strat, and in the case I really need to level some pet, I then (likely) exclude strats that are mentioning things like “RNG”, “risk”, etc. But: I’m always happy (when using a new strat) when I see some detailed infos, so that I can estimate what is going to happen. But YMMV.
My main plan will be to focus on raw gold in the beginning. Then I will spend my gold on leveling tailoring and enchanting so I can shuffle enchanting materials which is likely to be very profitable. I already have some shuffle ideas, and I will look for more. Then I’ll work on obtaining the rare enchanting and tailoring recipes to craft those for gold.
Warrior should be a go-to choice for everyone who wants to get into the end game. Protection Warriors in Classic WoW were considered as one of the best tanks, Fury talent build was a great option for DPS while Arms were dominating PvP environment. However, Warriors’ strength relies on the character’s gear, which means that you might need to put some hours into finding the right items for your class. It is also worth mentioning, that Warrior might be one of the hardest classes to level up in World of Warcraft: Classic but rest assured, if you’ll manage to hit the level cap and find suitable gear, Warrior is one of the strongest classes in the game.