Thanks martfox, you are really more than kind. I replied your PM.
For the others who are following the topic; here is the last situation;
- Thumbnails and other images are well set now. Approx file size of a thumb is 2kb-15kb.
- Homepage size is back to normal (around 2.3-2.5Mb)
- Total load time is not horrible. (Swirling around 3s-5s)
- CPU usage of PHP (whether CGI or FPM) is so high. (And sometimes MySQL CPU usage is high too.)
- Wait time is too long. (a.k.a TTFB)