Answer plz.
Optionally this feature can be enabled. If you enable it you will need to send cache-control: private on any requests you wish to not cache (also any responses containing set-cookie -- cookies will not be cached)
Answer plz.
I cant estimate based on those statistics. The best way to estimate (if you are using a control panel) is to get your bandwidth usage times times that by 2 (worst case, for most people its less than 1 due to gzip) and add on the cost for the IP.
For most people it works out less than $5 a month.
For you I would think you to be under that (even more so if you use an alternate sub domain for images and static resources as that greatly reduces bandwidth usage through our service)
Yes, you need to install mod_rpaf (Apache) or ngx_realip (nginx) or use the php code. See the first post.