is there any baseline rules about changing rotors? can you change rotors without changing pads? what does bedding pads/rotors involve exactly? need some help here. definitely need new pads, but possibly new rotors. thanks in advance!

If you can afford to, change both at the same time.Don't use old pads on new discs as you can shorten the life of the disc.If your discs are badly scored or have rust/grooves around the edges where there is no pad contact,then you are losing braking power.
When bedding in,I usually take it very steady for around 300-500 miles using the brakes more than I would normally but not pressing the pad firmly-just braking earlier than normal.I helped my dad bed some tarox discs and pads on his vw golf and the instructions specified to get the discs very hot from new to heat treat them(dad was scared to,to me it was perfectly normal;))Not all manufacturers reccomend this process though.
Rear discs take longer to bed in due to doing less work than the fronts.When bedding rears in,I just drive as normal.

You don't need to change both at the same time. Although if the rotor is grooved/scored you probably should. Try to break in new rotors on old pads if you can.

The old pads will have taken the profile of the old discs-using them on new ones will reduce braking force and take longer to bed in.If you must use the old pads,run them down a belt sander(wear a mask)to flatten them off as best you can.
Personally I would never use old pads on new didscs unless it was an emergency.Pads are the cheaper parts(usually) so I do both at once.

I just changed my factory rotors to slotted rotors. The directions specifically said to also change the pads at the same time. I dunno if that helps at all....

Mike