Design & Program WP Multisite(Only Wordpress Multisite Experts)

please note: Only wordpress developers & wordpress multiste developers know what I'm talking, So if you are either a wordpress developer or wp multisite dev, please don't consider reading the rest!. Well, I've a wordpress multisite installed on my website. As WPMU offers multiple sites facility, I've created various multiple websites each different from other and added to each site a unique theme. Each site has a unique purpose and so is the Theme. However, as my website is a unique portal of various services(sites), each been served from a single Domain, each site inside the wp multisite network has to be customized in such a way: every site must contain the main navigation links(apart from the links each sites' theme come-up with) and Homepage headerpart+logo. To put this in simple, my requirement is: 1) I want to customize all themes including the Homepage theme and put the Home-navigation links+Header part+Logo in all other sites inside the network, but keeping the rest of the theme/layout of each site as they come without disturbing each themes' functions/features. 2) Make/customize the Home-page theme reflect/publish all posts (including homepage theme + other sites themes posts) that are published under other sites in my network. 3) Put a Registration form/Login form on every page and site(apart from those that comes with default signup) inside, so users can Register or Login to get access to every site on the network. I've already collected necessary plugins & tools to do the above functions but I need some good WP developer/designer to customize & apply all themes+plugins to my requirement. If anything sounds unclear or you want more details please let me know.. Look forward to your replies.. Thanks..