1. I would say most definitely if you are diving on a frequent basis. Sensors are expensive, and despite a few tricks for prolonging their life, once the membrane has been exposed the clock is ticking down. If you are not analyzing your own gas, be sure to carefully watch whomever does it for you at your LDS to ensure a proper reading, and even then I would opt for a much lower PPO2 to avoid the effects that errors can have underwater (read, not everyone in a dive shop knows everything about what they are doing, and consumables like oxygen sensors often get pushed to the max before being replaced.)
2. Never pass 100% oxygen through any piece of equipment that you have not personally verified to be compatible for oxygen service. However, unless you are breathing high O2 mixtures, your regs should be fine. The real problem comes from high concentrations of O2, such as you would see hit the valve and cylinder doing partial pressure fills (the regulator is not being utilized during this process, so the only thing that matters there is the final percentage of your mix.) Personally, I would most likely rebuild the regs (if I had not done the last rebuild myself) to ensure that they were clean, free of hydrocarbons (silicon based lubricants), and utilitized EPDM or Viton orings, but then that is just the way I like things (there are several divers diving such rigs without employing these extra precautions.) It is certainly something to keep in mind the next time your regs need to be serviced though.
3. Find the cylinder setup that fits your style of diving, just keep in mind the various trade-offs that were mentioned in the other threads.
Please note that this is my personal opinion; I am not a professional and have no desire to be. I am just a diver who is continuously learning and having fun.
Something else to keep in mind is that we seem to be seeing more folks who are somewhat susceptible to elevated PPO2's. For year's it was thought safe to use 1.6 at rest (deco) and 1.4 during the working portion, but a couple of folks diving these numbers have not been so fortunate lately. Go slow and have fun.