Check to see if they have grooves cut in them. Rotors usually have a spec imprinted on them that you can check with a micrometer. If you do not feel a vibration when you are brakeing then may be good to go. Vibration usually means warped rotors.
Premium pads last longer regardless of what type of rotor you have. Besides, rotors are relatively inexpensive.
No. Unless you plan on taking a brake line off for some reason.
That's up to you. If I have it I usually use it. What can it hurt?
It should be mentioned here that this is one of the services performed by an automotive machine shop (at least a limited subset of those functions is available at some parts stores) and they have some ability, limited by specifications, to true 'em up a little if necessary. They also do sort of the inverse operation to brake drums, but that's another project for another day, if indeed you have them.
If they are warped beyond specs or damaged, you'll have to get new ones -- trueing them is done by taking off metal, and the shops are only allowed by law to take so much (besides which, if the rotors got too thin they'd just warp all the more easily and you'd be right back where you started). The main symptom of warpage as made manifest to the driver is a juddering feel when lightly applying the brakes -- it is easy to visualize exactly what causes this.
The logic behind this is, you only need to bleed the lines if you've introduced air bubbles into the system. That's what bleeding does -- it exorcises air bubbles. So if you are replacing the *calipers* or the rubber part of the brake line, or screw something up and make the pistons and brake fluid come out, you have to bleed the system, but if you are just replacing the pads and leaving the hydraulic parts assembled, you don't. A good rule of thumb is that if you see fluid, you have to bleed.
Bleeding can be done at any time; there is no need to disassemble the brakes. I'm in the "yes" camp when it comes to brake fluid changes every few years (admittedly a topic of controversy hereabouts). If you have antilock brakes, consult a repair manual for the correct procedure. Also, don't let the fluid level in either reservoir get below the minimum mark or you'll suck air in from that end and really have to bleed and bleed and bleed. Finally, a hand vacuum pump like the Mityvac is your friend during bleeding procedures. But I digress.
One other thing -- You'll probably have to gently push the pistons back into the calipers a little to get the newly loaded calipers back over the rotor. I've generally used a big "C" clamp, the sort carpenters use, and a couple thin pieces of wood to distribute its force evenly over the pistons. Unless you're built like King Kong you probably can't do it barehanded, and the temptation to use big slipjoint pliers has always made me worry about caliper damage. Once you've shoved them in, they'll come back out some (that's why you needed the clamp), but slowly enough to give you time to do the job.
Other things? Don't dangle calipers from the brake lines; suspend them with a coat hanger or somesuch. Whatever you do to one side, do it to the other. Contemplate the job and make sure any specialty tools you need are on hand before you disable the car. Wear safety glasses. Make sure the car is immobilized and is on passive supports such as jackstands (not just the jack) and generally not going anywhere before you put body parts into crush or pinch points. Have rags and hand cleaner handy because although the job is not physically or conceptually diffcult it can be rather dirty (you'll encounter hidden reserves of that nasty stuff that's so hard to wash off your mag wheels). At the end, take a slow test drive under relatively harmless conditions, and enjoy what'll probably be a rewarding and successful project.
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