New guy, cannot find enough information, quick questions

Hi there guys new here. I plan to buy a 5-7 in the near future, hopefully within 2 months and was wondering if you could help me out with a few questions before I purchase it. Couldn't find the right answers after googling a few months. How many rounds can this gun go through its service life? How is the reliability of this gun as far as dropping it and would it discharge/still function? How is the polymer compared to Glock and HK? I had a Sig Pro (might be a lemon) but the polymer on the frame easily scratches, even with my fingernails. I live in CA and the only rounds I can find are the American Eagle 40 grain and SS197SR rounds. Which one is better for home defense as far as stopping the threat most effectively? I already have a Glock 20 and Kimber 1911, so just wondering about this 5-7. Thanks guys.