Looks like we'll have to wait for xSystray :).

Backgrounds: use xLabel to hook it into, and have a magic pink background. !Labelrefresh can take care of the BG image.

Titles: Huh, so systray items have more than class names? Isn't that what the taskbar is for?
Sorting icons: no clue.
Changing icons: no clue.

Overall, I think you want to make a taskbar out of the systray. Poorly designed apps use the systray instead of taskbar, and ultimately that is your problem. The systray is fine for rarely used background apps and keeping track of some things (AV, connection status, CPU temp, etc.), but why other programs like to go there is beyond me.

Now, if you want to use it that way and use apps that will also go to the taskbar, look into xTaskbar.