Outside of just stacking a warrior with talasites because they have crusader are there any guides to gearing for 3s effectively for the other classes? or is it just the same as random BGs?
I actually wouldn't recommend talasite stacking on pretty much any class. There's not a gearing guide, but I can offer my 2 cents on arena gearing.
1. Gear for the comps you plan on playing.
If you're planning on playing KFC (Arms/MM hunter/Healer), you're probably going to be the easiest target for most opposing teams to hit. You could gear and gem to end games as quickly as possible with mega crits, but realistically it doesn't matter whether your sudden death execute crit hits for 2400 or 2800. The extra damage is more than offset by the risk you create by having substantially lower health.
But for something like Warlock/Warrior/healer? You'd feel really clunky running around with 5k health when every enemy team is trying to kill your warlock. Think about stuff like this in advance - it does make a difference. If you're able to have one squishier set (2-3 talasite max) and one bulky set (7-8 talasite), that would be ideal.
2. Gear isn't the most important survival tool.
There are actually quite a few other things going into it. How coordinated are you with your healer? You could be a 6k health Tauren Fury Warrior and drop like a rock if he's running around the wrong side of a pillar to heal you.
Do you have good trinket options? These are technically gear, yes, but so few people have taken the time to get their Ember of Nullification (Black Rook Hold, 2nd boss, requires tank spec or trade) in the practice games we play. Having access to a small handful of trinkets depending on the team you're facing is absolutely critical.
Are you positioning correctly? This is a big one. If Arms' goal in an arena is to find that critical moment where the procs align, does having consistent damage really matter that much if it's ultimately not needed? You don't need to stand in the middle of the map and whack on a mage that you're not going to kill without procs. That type of playstyle will get you killed more than anything - find the right opportunities, otherwise don't make yourself an easy target. There's more nuance than just pillar humping until sader/death are up, but it's worth thinking about how you actually win a game with your team and playing accordingly.
3. DPS Gems / Enchants
... are largely up in the air and/or player preference. I couldn't tell you what is best, other than to say that 2/2 str/crit gems or +3 str gems are probably what you want to go for. Yes, I know that crits are only 150% in pvp - but we're talking about arena, not a dps dummy. Big yellow numbers are how you kill people. Make those big yellow numbers happen as much as possible. Doesn't matter if they're 125%, 150%, or 200% damage. That being said, I can also see an argument for +3 strength gems. I think it's largely preference.
Hope this helps!