[TYPO3] efficient multisite management?

[Frank]

Hello,

We are building a project where we have a main (national) website (two 
languages) and several sub-websites (regional). We have reproduced a 
sub-site, by exporting t3d. But IMHO this is not a very efficient way to 
proceed?
Since all sub-sites are derived from the main site (the sub-sites have the 
same basic style, have only some of the functionalities of the main site 
etc) then it should be possible for example to produce a search page on the 
main site, and use a sort of 'instance' of this page on the subsites. The 
logic is that whenever I would change the search page, then this change 
would automatically be visible on the subsites also. Otherwise I would have 
to reproduce every small change on all subsites, re-export the t3d and so 
on.
The same logic goes for the templates. How to make a cascade of templates 
and parts of templates?

Can anyone give some hints?

Greetings
Frank Sonck