Yes it will get it. Was already announced as one of the devices that will get it. Probably 2-3 months after the new nexus devices at the earliest. It'll vary by carrier as well in terms of timing. Can't comment on the security fixes. I mean how do you know if a security fix is fast or not. If they don't release a patch for 3 months. What does that mean? They took a long time getting one out or that was the regular schedule? These are also carrier dependent too.
Yeah they are pushing the security updates to flagship phones on carriers every month with a few exceptions here and there.
It'll receive Nougat but not anytime soon. Samsung has to finish their development and test, then our wonderful carriers have to test their part. I'm thinking earliest will be end of year but it may be early next year as well. But most of the user facing Nougat features are already in TouchWiz so it isn't that bad.