Populating Listings on Network of BP Sites by Category - MU/BP

I'd like to setup a BP network of sites as follows.

PARENT SITE

-domain.com

CHILD SITES

-toplevelsub01.domain.com
-toplevelsub02.domain.com
-toplevelsub03.domain.com
-toplevelsub04.domain.com
-toplevelsub05.domain.com

CHILD SITES NICHE SPECIFIC

-bottomlevelsub01a.domain.com
-bottomlevelsub01b.domain.com
-bottomlevelsub01c.domain.com
-bottomlevelsub01d.domain.com

-bottomlevelsub02a.domain.com
-bottomlevelsub02b.domain.com
-bottomlevelsub02c.domain.com
-bottomlevelsub02d.domain.com

-bottomlevelsub03a.domain.com
-bottomlevelsub03b.domain.com
-bottomlevelsub03c.domain.com
-bottomlevelsub03d.domain.com

-bottomlevelsub04a.domain.com
-bottomlevelsub04b.domain.com
-bottomlevelsub04c.domain.com
-bottomlevelsub04d.domain.com

-bottomlevelsub05a.domain.com
-bottomlevelsub05b.domain.com
-bottomlevelsub05c.domain.com
-bottomlevelsub05d.domain.com

ideally i'd like someone to be able to post a classified on the main domain site which would also populate on 1 child site and 1 niche specific site.

i'm hoping i can get some direction on how to set up the categories and overall network so when posting a classified the user selects ie.

03 and separately c.

Therefore I'd have one page of all classified listings on domain.com, then a duplicate of that listing on toplevelsub03 and bottomlevelsub03c.

I'd of course only like those who have signed up to post a classified but be shown to unregistered users.

secondly, i'll want to have another series of classifieds users can post that can only be shown to other members within a "group." :disappointed: make sense?

i think the biggest challenge i'm having is understanding how the categories and taxonomies work....