I'm a wordpress newbie and I'm having few serious problems

Hi,
I'm a wordpress newbie and I'm having few serious problems that I'm not sure how to solve the best way.

Here's the background:
- I want to have an open registration multisite for my website (as a stand-alone addition to a large forum).
- I have to have a common admin-bar with login/register links and a link to a start page.
- I want to use at least two different domains to choose from. One of them is defined as a wordpress domain. Another is defined in Multi Domains plugin.
- I want to let my users pick wordpress theme
- I earn money with ads
- I want to have a Pro level paid subscription
- My users are not internet savvy. I must have it working as simple as possible.

After few weeks of tries and tests I have a more or less working setup using few of your plugins and a little of code found around. And few problems to solve.

Here they are:

1. Admin bar, mu-plugins and anti-splog
I've found a way to build an admin bat using mu-plugins code:
<?php
function pjw_login_adminbar( $wp_admin_bar) {
if ( !is_user_logged_in() )
$wp_admin_bar->add_menu( array( 'title' => __( 'Log In' ), 'href' => wp_login_url() ) );
}
function custom_adminbar_menu( $meta = TRUE ) {
global $wp_admin_bar;
if ( is_user_logged_in() ) { return; }
if ( !is_admin_bar_showing() ) { return; }
$wp_admin_bar->add_menu( array(
'id' => 'Register',
'title' => __( 'Register' ),
'href' => ust_wpsignup_url(),//wp_registration_url() before anti-splog
)
);
}

add_action( 'admin_bar_menu', 'pjw_login_adminbar' );
add_action( 'admin_bar_menu', 'custom_adminbar_menu', 15 );
add_filter( 'show_admin_bar', '__return_true' , 1000 );
?>

But ust_wpsignup_url() is empty. Is it because mu-plugins are executed before everything else? What is the best solution to have the admin bar always on (no matter the login / theme etc) and have a proper anti-splog link?

2. wp-login and multi-domains
i want users to be logged into their respective blog cockpit as soon as they submit the form.
I am using the followin mu-plugin:
<?php
function ds_login_redirect( $redirect_to, $request_redirect_to, $user )
{
if ($user->ID != 0) {
$user_info = get_userdata($user->ID);
if ($user_info->primary_blog) {
$primary_url = get_blogaddress_by_id($user_info->primary_blog) . 'wp-admin/';
if ($primary_url) {
wp_redirect($primary_url);
die();
}
}
}
return $redirect_to;
}
add_filter('login_redirect','ds_login_redirect', 100, 3);
?>
It seems to work fine on the main domain, but when the user uses the other configured domain, he/she is redirected to wp-login on their blog, to submit again. What is the best way to allow users to log-in into their blog from the main site?

3. I need to have 3 ads defined in head, header and a sidebar. Is manual editing of the theme files the best way to do this? This would seem a little redundant - as the code will be the same throughout the network.

4. One thing that seems to appear quite often, even on your support forums, is simplification of wp-signup.php. I really admire the edublogs - super simple, one page signup. Browsing the internet I've found that there are few ways to accomplish one page signup. One seems to be purchasing Gravity for 200usd, the other - editing a copy of wp-signup.php inside the theme folder. I'd rather not spend more money but I've tried to take a peek inside wp-signup.php and I got scared. There seems to be a lot of code inside. Can you give me a more step-by-step hint on changes needed to be made to this file, just to have it displayed on one page? Will it retain the ability to use blog templates selection after the edits?

5. Mobile
Is mobile skinning solved in each theme separately? Anything I should be aware regarding mobile and wordpress multisite?

6. Comments
I am already using disqus comments on another page and I quite like them. As I understand - users would have to register to leave comments under posts. Do you have any experience with disqus as a replacement for built in comments in multisite environment?

Thank you