How hot is hot? 7 leds running ~15mA each = 105mA, worst case scenario you multiple it by the number of display you have + few mA for your PIC.

Then you multiply it with the voltage across your voltage regulator (Vo-Vi), and you have the power dissipation for your voltage regulator.

Assuming you're running it from 12 volt, things can heat up fast indeed. Heat sink will help, but not always necessary.