Ah, the css problem may well be related the javascript that builds the sliders. It applies a load of styles the to content tab so that may well make the slider inactive when you've applied an external style...
FAQ Slider allows you to set the tab that is visible on loading the page. You simply add ?faqtab=n. This is demonstrated
here. You could set your cart to return to a dynamic address...
As for performance, well there are two factors: sever-side and client-side.
If you use the section syntax, all the data is loaded in one db query which is nice and efficient. I've just made some modifications that will make the plugin itself much more efficient.
The more tabs/sliders you have the more client-side work will be necessary to render the javascript effects. That's really the users problem. I think the FAQs on Trafalgar Design are starting to push it as it takes a second to render the tabs/sliders...
FAQ Slider has lots of advantages in my opinion like the ability to link directly to the article to edit it, lots of display parameters for the content in the tabs, nesting abilities, setting tab visible on display, loading modules as well as articles and event the ability to build your tabs/sliders from inline content.