[Mediawiki-l] Extensions and methods available to insert page elements to all new articles consistently

As most of the regular contributors to the list will know by now, I am total newbie to Mediawiki and having only just managed to successfully install it, I am still finding my feet. My question to all in this instance concerns that adding of page elements such as formatted tables, page dividers, and boxes containing specific links to given articles across one's entire wiki so that each article page conforms to a consistent look and feel. Looking around the Wikipedia website, I notice that there is considerable consistency in terms of how content is displayed. Within a given category page, there always seems to be a banner divider at the bottom of the page and key facts are often contained in a separate floating box. Within a biography page about a given person and persons, key biographical data is contained again in a separate floating box. It's these sorts of elements leading to a consistent look that I want to include in my own wiki. Now of course I could do all this by simply including raw XHTML code in every new article. However, for reasons I'm sure you will not need explaining to you, this is a far from ideal solution. What I wondered therefore is are there specific extensions available that provide the necessary functionality to include these elements? I realise that wikicode will provide some basic functionality but if I was say a floating box included in an article, I don't want to have to repeatedly include XHTML code. Equally, I don't want to have to create specific templates for specific categories unless there is no other options available. Rather, I'd prefer to let editors choose what elements to include in a given article page and how they appear (that is to say how they're formatted) but restrict the choice to a number of pre-set elements so that one does end up with a consistent look and feel. I apologise again if this discussion includes some very elementary questions but as I say, I'm just starting out. What I really want to know is how it is that the actual format as well as look of all pages within Wikipedia is maintained. There must surely be extensions in place that enable content to be displayed in a particular way. seem to be able to discern this for myself.