Just to add some informations about the slats :
-The extention to the midsealed position is fully mecanical from the lever in the cockpit.
-The extention to the full position needs electrical power and serviceable stall warning computers, as they will as already said extend to full positon automatically if a stall is detected. It is part of the checklist to check the slats going to full then back to midsealed even when the flaps are set to 13 and bellow. Their position is checked by 4 announciators TO LND DISAGREE and AUTOSLAT FAIL.
With the flaps T/O selector you can use variable flaps setting from 0 to 13 and from 15 to 26 degres. In my company, our performence is calculated by laptops and the position we use the most is 7 degres. But it can happen that we use 5 or even 26 depending where is the performance limitation.
Taking off flaps less is not a big deal, exept you might do a tail strike. For exemple the difference between V2 and Vflaps is 5 knots only for flaps settings below 13 degres. Vslats is usually more than 35 knots above V2.
I am pretty sure an MD80 would T/O flaps/slat less, until living ground effect...