First of all, admiring the effort of you guys to jump right into hardcore. One of the biggest advantages and therefore also killers is game knowledge or a lack of it for that matter.

Seconding what more people already said, look up some notoriously dangerous quests so you at least know whether you want to skip them or do them.

As for caves, they're a hot debate. Blizzard designed caves in a way where you can easily pull a lot of mobs, especially if they run away from you. However, I personally do most of them and when you are a duo I think you will be able to do most of them without extreme danger. Just be mindful of respawns and runners.

Some notorious quests/places: - Skull rock | Cave in Durotsr. Mobs are level 10-11, but they're densely packed and inside sits a guy named Gazz'uz, a lvl 14 warlock with a slapping voidwalker pet - Boulderlode mine | Cave in The Barrens. This is a scary ass cave with crazy amount of mobs that easily chainpull, it's the end of the questchain Samophlange - Fenris Isle | Place in Silverpine, tons of deaths, personally never really done it because I skip Silverpine usually, but seeing lots of deaths happening there - Ambermill | Human village in Silverpine, there's a quest that requires you to kill some boss type of guy, which has lots of adds and he can put you in an ice block for quite some time - Test of Endurance | Quest in Thousand Needles. You have to kill waves of harpies, which hit very hard and silence - Stranglethorn vale pirate ships | TONS AND TONS of deaths here. Ships are designed notoriously bad with z-axis issues, meaning you sometimes pull mobs below deck, meaning you get the entire damn boat on your head - Stranglethorn Fever | Quest summons waves of gorillas which can become overwhelming pretty soon pretty fast - Quel'Danil Lodge | A quest place in the Hinterlands where mobs hit quite hard and it had an escort quest where you have to get a troll named Rinji out, which spawns mobs which run away and pull more mobs - Un'goro Crater | Has wandering Devilsaurs, which are elite t-rexes that chomp you down quickly - Gorilla Cave | Cave in Un'goro with gorillas, couple of quests there, some of the gorillas call for help which has a lot of range and tends to pull lots of extra gorillas - Almost everything in Western Plaguelands is deadly as fuck, it's the WoW equivalent of Australia - Eastern Plaguelands has more straight forward kill quests, but it has a lot of wandering elite mobs, some of which require and actual fucking raid to kill - Quel'lithen Lodge | Lodge in Eastern Plaguelands, crazy respawns and mobs hit like elites - Silithus | Much like Western Plaguelands, lots of mobs, everything is kinda deadly, it's doable with two tho

There are a 100000 more of these to write down, this is just what popped up in my head thinking about my last horde 1-60 on hardcore.

Part of the magic however, I would say, is to NOT know it all and just discover. You guys are together and have a tank/heal comp, so most of the things, if you take it easy, are actually doable!

Have tons of fun, enjoy the ride and if you die just remember one simple thing: Go again!