Hi there,
While I cannot provide a comprehensive answer to all of your questions, I can provide you with my own experience concerning titanium: I've had titanium rods, plating and screws lining the grand majority of my spine for 8 years now. I am happy to report that there are zero complications or discomfort for me, and from everyone else I have spoken to who has gone through a similar experience, they feel the same way. My doctor told me that the only complications he really ever encountered were infections (which happen very soon after the surgery, and are a risk with any surgery), and physical discomfort with the correction devices a few years down the line - which he insisted was extremely rare and only occurred in exceedingly thin people.
From what I understand, my doctor is one of the best orthopedic surgeons in the world and has been in practice for several decades. I recall asking him if there was anything to be concerned about regarding the metal in my body, and he said that he had never encountered a problem before.
I hope this is helpful. I'm sorry if it isn't particularly informative, but I can only hope it provides some level of comfort.