Hi there

1st of all, I found your support just awesome and I like to share you my misery to help me with it please , 2nd I'm so sorry if I knocked a door which was already opened.

but I searched around for an answer but with no avails

I'm not an expert in php coding or master in web designing but I'm building a medical website which is proudly using press services, WPMU, BBpress and Now I wanna Add Buddypress.

I searched around for how-to install buddypress as a sub-domain
I'm using wpmu 2.9.1, wildcard is active and I like the install buddypress as

Community.example.tld

rather than Install Buddypress on a Secondary Blog --> (http://codex.buddypress.org/how-to-guides/install-buddypress-on-a-secondary-blog/)

I've read Changing Internal Configuration Settings --> (http://codex.buddypress.org/how-to-guides/changing-internal-configuration-settings/) but didn't find a clear answer.

I came across this code if I like to Set which blog ID BuddyPress will run on:
define ( 'BP_ROOT_BLOG', $blog_id );

if I didn't find an answer for my first question, I have plan B question ;)
if I've chosen the blog Id to be 3 for example
would it be like this blog3.example.tld/community

and How can I Keep my old BuddyPress user / group avatars in the 1st and 2nd situation ??
and How to Redirect previous BuddyPress permalinks in both cases

I'm sorry again if I asked for something which is already answered but you are my 1st and my last rescuer

Thanks again