Kramerican, I think I will be able to help you. We're specializing in highly customized Elgg websites. I already did a few development plans and a few dozens of audits on Elgg-based websites. We can help you with advice as well as scaffolding of the main custom plugins. I just sent you a PM with details.

event calendar

http://community.elgg.org/pg/forum/topic/683614/ni-help-integrating-a-semicomplex-elgg-site/

groups plugin is available in the mod folder of the default elgg install (1.76)

izap video (requires ffmpeg - im using 3.81b with elgg 1.76 but theres a new one just out a few days ago)

http://community.elgg.org/pg/plugins/release/604143/developer/izap/10-more-reasons-to-upgrade-to-izap_videos-38b-25oct2010

target blank (puts external links in a new window - obviously)

http://community.elgg.org/pg/plugins/project/522433/developer/jeabakker/target-blank

message board plugin comes with elgg in mod folder as does the bookmarks plugin.

wall to wall plugin for the messageboard plugin (ala facebook wall)

http://community.elgg.org/pg/plugins/project/384546/developer/costelloc/wall-to-wall-messageboard-addon

you can use the permissions system to set up your six groups and keep them apart on a single install of elgg.

use the api to get the data out of elgg and into your external site.

you would need the file plugin aswell (in 1.76 mod folder)

chat and notifications

http://community.elgg.org/pg/plugins/project/385039/developer/alchamist/elgg-bottom-bar

when you get a message you get a notification of that message, users can set  notifications by email.

Mike knows what he is doing and can help you.