So I had some time on my hands this morning and decided to play with Gildar's map. As I told him, I basically took it and photoshopped the heck out of it. Not sure if anyone will find this helpful or not but it was a good way to kill a few hours on a Saturday morning. LOL
There's much more to tactics for the Citadel than just where to get the keys but, as uoguide says, a stealth mage is an EXCELLENT choice. Especially when you are learning the layout. Personally, I think some form of stealth character is almost essential to learn your way around Citadel. Also, remember, circle of transparency is your best friend in Citadel.
Anyway, here you go, from easiest room to hardest:
Yellow Key
Blue Key
Red Key
Good luck!