Need some help creating a multisite cluster

hi guys , some 6 months ago i discovered wordpress,is fantastic & i started doing all my websites using it , but now im in a bit of a problem & i need some help
so here it is :

im running multiple websites with pretty much the same content

ex : http://ambulantadiacena.ro / .com / . info
DiaMedShop.ro etc ….

there are more than 20

so is frustrating to update the content in each of them using multiple databases & cloning the original & modifying it to change the domain name

im interested to use a network feature where i can login as a super admin & :

add post on multiple sites at once , or just on specific grups of websites
configure different themes & plugins for different sites
etc

while website visitors see a different domain name for every website
for the moment websites are grouped in clones , but for the future in want to add some different content to each of them , while i keep some of the content common to all of them

also very important i dont want google to index this a one big site because then i will have problems showing up in search results

…………………………………….
FIRST OF ALL I WANT TO KNOW IS THIS IS POSSIBLE USING WORDPRESS , or there is other option i ca use ?

if is possible , where do i start & what can i do

i have a medium knowledge of php, java, html, css

i would appreciate if an advanced wp user can tell me if all this is possible so i dont waste my time trying to doit considering im not an expert or something like that …..
if is possible & others have done it then i can give it a try