Is Non-Passive Cooling bad for Lithium Ion Cells?
Your concern is somewhat misplaced. At 1 A charge-discharge, normal 18650 Li-Ion batteries do not heat up. Consider that normal battery heats up only due to Joule dissipation over ESR, and the ESR of most 18650 cell is under 100-150 mOhms. So the maximum internal dissipation is under 200 mW, which, for the physical size (and surface area) of 18650 cell is nearly nothing.

However, since you plan to discharge them, you will have full 4 W dissipation in each of your loads, so a fan blower will be a must.

Car batteries gets discharged (and charged during recuperative braking) at much-much higher rates, and only then the internal dissipation/heat generation becomes an issue.