Minions

Keep in mind, higher tiered minions can teach lower level minions, like a diplomat training a construction worker to be a valet, so keeping your minion roster higher tiered heavy is a good idea. Maximum minion capacity (without modding) is 100. As you do evil in the world you will increase the number of minions you can maintain naturally without lockers. Lockers act to let you exceed this number quickly. It's possible that you could be so evil that you don't need any lockers in order to have the maximum number of minions, but I've always beaten the game before I got there. As you research, you'll also unlock "Double Lockers" which take up 2 squares but provide (I think) for 4 minions. Send your Evil Genius to the areas where your minions are standing around like dolts and have him/her execute a construction worker that isn't stupefied. That should give the stats of every minion a healthy boost and get them all back to working.

Construction Worker

Only Construction Workers will build new rooms.

Only construction workers and valets can go fetch the items you order.

Use pistols.

Technician

Only technicians can repair your base (higher level science minions must consider it beneath them).

Valets

Only Valets can put out fires.

Only construction workers and valets can go fetch the items you order.