One last thing, often its assumed that since it is lower level content you don't need to be hit capped or exp capped because the bosses are lower level. This is not true. All bosses, whether 60 or 90, act the same as far as dodge/parry/block goes. 7.5% hit and 7.5% expertise is recommended. With 460 gear you probably won't be able to reach these marks, so aim for 7.5% hit while getting expertise as high as you can.
To get to KT, you do not need to clear any bosses. KT is not gated. However, to use the strategy posted later, you should kill Al'ar and clear all mobs you come across before and after him. (Disclaimer- if you are geared enough, you can stealth to KT, avoiding all mobs except the ones in his room and kill him there.)
For killing KT only, you can avoid any trash that doesn't impede your way back to the start. For clearing the instance, any trash in the bosses' room need to be killed. You can wait until all trash despawns after killing the first three bosses and kill all trash leading up to KT, or you can kill trash on your way.
- Al'ar- Easy
Al'ar is the first boss in Tempest Keep. Clear all trash in his room. Once you do that, aggro the phoenix by using deadly throw, and he will go to the first platform (the leftmost platform in his room as you enter). Get to him on that platform and dps him down, should be fairly easy. After you get him down enough, he will move clockwise around the room, and you should repeat this task. Once you defeat him on the last platform, he will spawn in the middle of the room. Dps him and kill the adds when they spawn. Another easy phase and you should have him down fairly quickly.
- Void Reaver- Easy
Make your way to the left most corridor of the instance. You must kill all trash in Void Reaver's room before you pull him, otherwise they will aggro. Void Reaver is another easy kill, just keep recup up and dps him down, should be no problem.
- Solarian - Easy
Solarian is the right most corridor of The Eye. Go to his room and kill all the trash surrounding him. The stationary trash along the walls are very easy to kill. There is a pack of trash towards the middle of the room which mind control, and may result in disconnects. Kill these trash as fast as possible, target the Nether Scryer and bring him down asap, he is the mc add. If you happen to get mc'd and dc'ed, don't worry. You'll zone back in and be able to try again.
As far as the Solarian fight, it's a very straight forward fight. Kill the adds when they pop and burn Solarian. As always, keep up recup and use leeching, kill adds when they spawn.
Kael'thas Sunstrider- Difficult
KT is tricky. With the strat given (for low ilvl characters) you need a clear path to the instance entrance. So, kill all adds to clear a path up to KT if you haven't already. There are 4 phases to this fight, first phase deals with his minions spawning to try and kill you, second phase deals with some swords, third phase is his minions spawning again all at once, and fourth phase is KT alone.
The toughest phase is phase 3, but the trick is that during P3 his minions spawn where they have died. So the idea is to kill them as far away as possible and force them to run to you. The strat is that you kill his adds as far away as possible, and they will have to take time to run to get you.
So, that being said, where you kill them during P1 is crucial. EQUIP A PVP TRINKET.
P1- run up and aggro KT. Once he starts his emotes, run back to the starting area, hide behind the first alcove. Hide behind the wall. Wait for the first add to appear. Kill him. The second add should be about a minute behind. Kill him at the same spot. Careful with him though, he will fear you, make sure you are far enough away that he won't fear you out of the instance. Once you kill him, run back to Al'ar's room. Go the the ramp to the right, and sit just out of los of the second level, basically a couple steps lower than the second level. The third add is a mage so you want him to come as close to you as possible. Make sure your back is to the wall and fight the mage there, he will knock you back and the worst thing to do is have your back facing the open room. He will disorient you for 10 seconds periodically as well, just keep recup up and you will be fine. Once you kill him head back to KT's room and you will eventually meet up with the engineer. His ability puts a debuff on you which will randomly stun you for a few seconds. It's impossible to counter, just have to deal with it. He doesn't do much damage, just try to kite him to the hallway right before KT's room and kill him.
P2- Sit in the hallway where you killed the engineer. KT will emote a bunch of stuff and will eventually spawn a bunch of swords. I advise going combat for this fight, which I was when I killed him. Pop blade flurry and kill theses swords asap. Don't pop cd's, you have a minute to kill them and should be plenty of time.
P3- This is where your positioning in P1 comes in handy. The adds will spawn all together, but will have to run to get to your spot. First up is the engineer you killed closest to you. Burn him down quick. Second up is the mage, if you have to pop some cooldowns, the mage needs to die fast (I didn't need cds). Third and fourth adds just burn down. Once they are down KT will emote some other crap, just sit in the hallway where you killed the engineer and let him come.
P4- This is where it gets tough, KT will come to you. Keep recup up and shiv for leeching poison proc every chance you get. Kick every pyroblast you see. Pop blade flurry again for the adds. Once he gets to 50% he will go back in his room and do some more emotes. When you are able to target him again pop every cd you have (adrenaline rush/shadow blades). This is the burn/gcd phase. Kick pyroblast every time you see it. Try and burn him as fast as possible, he adds a stacking debuff that diminishes your health. When I killed him I had so little health some of his abilities were doing about 50% of my hp. When you get low, use cloak/evasion/combat readiness. Prep and do it again. This is also where trinket becomes handy, he will disorient you periodically. Try and save trinket for when you are low and need to use a defensive cd. Burn as fast as you can and survive. Don't get discouraged if you die, a lot of rng has to do with killing him. Keep with it and you'll get him down.