You should be able to go to the component page in the admin and choose the full width page template. there is a drop down on a pages admin in the right sidebar to choose page templates
If you’re using a twit login plugin then you need to blank out the part in the admin for that plugin that adds that to the username. Each and every time you change the settings on that plugin make sure the username box is empty. As for changing the usernames: http://buddydev.com/plugins/bp-username-changer/
The easiest way is to ask the question in the profile fields section and then block the field from showing in the profile loop instead of messing with the username password.
In bp-default/members/single/profile/profile-loop.php find the profile fields table and change code accordingly.
You can then output the info on the members profile but wrap it in a if_is_admin statement and then only the site admin will see what the user has inputed into the field.
oh and you could use theme switcher plugins to change a site wide theme to predefines styles. Create little thumbnails like twitter and when user clicks image it switches to that theme/style.
I don’t think you will find an easy solution to this. The user nav is directly tied into the members component just as the groups sub nav is on the groups pages.
Try looking in to the admin bar code that shows the user nav links.
The beta 3 should be ok to run on a live site. Always back up though before installing beta BuddyPress. You will get native drop downs and many other fixes/enhancements
Plugins are better because then you have options as apposed to only having what is in core. BuddyPress comes with a set of core components but each of these have hooks, filters you can plugin into and craft anything your coding skills can muster.
You can use the profile part or maybe you just need groups. Pick and choose what you need to make it work for you.
The BP template pack plugin is there to help you integrate with a regular WP theme.
