Making a Sandbox Server! Any tips on which plugins and addons to use?

Here's my "must have on Sandbox" list:
ULX - no other admin addon can replace it IMHO. Glad you already have it at your list
Wiremod is another awesome mod, it contains many electronic components that allow you to build more advanced constructions
Advanced Duplicator (1 or 2, I prefer the first version) - can help manage your constructions like saving/restoring
UClip - cool small addon that blocks non-admins from flying through the walls and possibly crash your server with unseen propflood
sui-scoreboard - advanced scoreboard with rating system Very cool