Looking for input on this issue ...

I changed out all the pads in my 85 300D this weekend. Three out of four wheels looked normal. Pads were worn. Rotor ok not great. BUT, the left front unit was toast. The pad material was crumbly. The pad housing was nearly impossible to remove from the caliper. I completed the job. The performance is WAY better but there is still a noticeable brake shudder at high speeds. Now I am wondering ...

1) If I now decide to change the front rotors, how soon need I do it before the new pads are too old to put on new rotors?
2) Is it possible a faulty LF caliper caused the pad problem? It seemed heat damaged and the pad housing was corroded.
3) I did notice that the rubber boot on the caliper piston on the RIGHT front caliper was disintegrated (the boot you see when the pad is removed and the piston is all the way out). Is this a sign that my calipers need an overhaul? Or can I work it out. There is no pull or other blatant brake problem.

Thanks in advance.