There are a few on addons.opeera.com ... they were called "skins" and searching for that term brings up the few they have (and a few themes that just happen to have the word "skin" in the title, of course).
indonesian, i know it about that ...the single problem is that i don't know how to add a custom bbcode, something like this i need [center][img] img link[/img][title=blue]title[/title][/center] and further on if i want to customize this code i dont see any option
Yes, the default time is 3 hours unless the RSS specifies different time. You can also change this time manually by clicking on a feed with right mouse button, selecting properties and changing "Update" time.
Sure it's possible. It's like when you first install operating system without any additional software. It's running fine (sure depending on hardware, ram,....). But as you add more custom applications and services in time like Antivirus, Firewall, ... then system will became slower.
It's the same with extensions. If you install more of them, they can use more RAM, or even more CPU. Still it's also question of what exactly is extension doing. Some can "only" reserve more RAM, but use CPU time only on user action. Some can interact with pages/tabs, so they will use more of resources. So some you won't even recognize, but some can degrade your performance.
You can also see some of statistics in options. First you need to enable Developer Tools at: "More Tools > Enable developer tools". Then open statistics "Developer Tools > Task Manager".
Not that I'm aware of. i urge it here in this add-on forum as a useful keyboard-shortcut feature for for an Opera add-on.
You might want to post a request for this type of keyboard functionality also in the Suggestion forum for an Opera feature. You could mention that all the other browsers provide that shortcut as part of the native browser, and it is useful.