Check out GimpShop if you are looking to use GIMP, it is GIMP with a Photoshop-like interface.
There are probably some personal DB options that use SQLite or something, but I would personally recommend either a MySQL/Postgresql/ODBC combo, which would enable you to use any ODBC savvy app with these DB backends, or a MySQL GUI such as Navicat. There are a ton of different options and combos here, but I would definitely encourage something SQL based, as the SQL query language is far more open, and useful with a number of DB backends.
You'll have a much harder time replacing graphical apps like InDesign and Illustrator. The OSS seems far more interested in developing smaller tools that work together than they are in replacing big monolithic things that are already well-established (with some obvious notable exceptions).