I have a similar setup for your bigger girls - heatmat is the main heat source, they are literate by a combination of an overhead spotlight (so not a ceramic) and LED. My other tanks are lit by LED and heated with mats.
The girls rarely bask in the spotlight, but do occassionally. What's interesting is that Vlad doesn't have a spotlight any more, but used to have one, he's lit by a strip of LED and I fairly frequently find him in the overhead vines laid out along the length of the LED strip. :-)

Thermostat - a dimming is an on/off whereas a pulse proportional modulates the power to provide a more accurate temp. For garters, I don't believe that you need the accuracy of a pulse prop stat, a dimming or mat stat will keep the temps to within a few degrees.