I'm with Ron_L in this. KISS and you will be happy. I'll add a couple more suggestions.
First, try to keep temps from going too high at the start. Look up "Minion method" for starting charcoal (put a relatively small portion of lit charcoal on top of an unlit bed to get things started.) That will help to keep temps from running away.
When you close up the smoker, close two of the three bottom vents. That should provide plenty of air. In fact, on my first smoke on my 18.5 it was leaky enough to hold 250° with all bottom vents closed. As smoke residue builds up, it will become easier to control.
Do use water in the water bowl to help manage temperature. Lots of more experienced cooks here will recommend a foiled clay saucer or similar and I suggest getting comfortable with temperature control before you try that.
Good luck with that first smoke! (and remember - pictures or we won't believe you.