What fixtures do you have available. It is no good us recommending fixtures, as chances are you will not have the budget to hire S4s or anything of the sort.
As a general rule, when working in the round I would divide the stage into 4 sections. Special in the middle of all four sections, and a special in the middle of the stage (specials being spotlights for monologues or highlighting charactors).
Then I would have 3 washes - Open white, hot colour and cool colour. Light each quarter on their own dimmer channel - since you have limited dimmer channels, pair the open whites, so that each half is on it's own channel. That gives you one channel spare for something fun.
That said, 16 channels seems to be a very weird number. Dimmer numbers are almost always a multiple of 3 (as they are usually powered from a three phase supply)... I would check that one out, as you may have 18, or even 24 channels. They could have told you 16 because they want two for houselights or something - if so, ask if they can possibly reduce it to 1 channel.