"Official" Installation Order for all related prod
This is going to be official as it gets.
Source Maps Castles
Tome of Ultimate Mapping
Universal Update 8
Source Map Temples
CHMP (Harn toolkit)
Campaign Mapper & the Forgotten Realms Atlas need to be installed after CC2 & don't forget that CM has a patch that is essential, otherwise you get the wrong symbols. The FRIA has 3 updates. There it's a bit fuzzy - the last one is supposed to include everything but I think it misses a few things. If you install all 3 updates, in order, make sure you clear the read only flag on the Maps folder before each installation, otherwise some maps won't get updated.
Really the rest of the add-ons don't matter, except Source Maps Temples - it has to go in after UU8. CHMP can be added at any point - it backs up & modifies the menus, so your best bet it to do it at the end.
FT is independent of CC2, so install it first or last - doesn't matter.
I've lost my copy of Overseer somewhere along the way, so I don;t know what it does or doesn't do to the menus. It should have a readme file that explains how to add the items to the menu if they get missed. I'd suggest installing everything else & then manually adding in the Overseer menu items to make sure they don;t conflict with later updates.