DISCLAIMER: I am not a doctor, and I have absolutely no medical knowledge or training whatsoever.
Considering manual exercises ONLY, and assuming that you are not trying to rip the head off your penis when you stretch or going to any other sort of extreme, I don’t see how “normal” PE could be a problem. Increased blood flow, more frequent erections, and better knowledge of your body and its responses can only be positives.
I have a fairly laid back and lazy approach to PE: I stretch/Jelq/edge when I can. If it doesn’t feel good or I’m just not into it, I don’t force myself and let the inches fall where they may. What I can say is that over the last month, even with my lazy approach, I have had better erections, more confidence, and better SEX than I have had in years.
In the beginning I was concerned as you are, and rightfully so: you only get one penis, and the idea of ruining it somehow is just about the scariest thing I can imagine. That’s why mechanical and chemical PE have no appeal to me. Now that I have been doing this for a little while, I think I might experiment with clamping some day, but only because after a month of becoming more familiar with myself and what is happening down there I think I understand Clamping and I think it could work safely.
The best thing you can do is READ READ READ. Learn from the problems others have posted, and try to avoid the same pitfalls. It seems to me that most people who did damage tried to do too much too early and ignored all the warning signs. Pay attention to your PIs, listen to your body, and above all have fun. (I like to chant “grow baby grow!” in my head when I’m Jelqing :D )
Best of Luck!