Welcome to ecf and congrats on kicking the stinkies to the curb.
About the nic level. Once you receive you aspire K4, is it a kit with a tank? I noticed some vendors include the Aspire Cleito as an Sub-Ohm tank. That particular sub-ohm tank with your 12mg should be quite satisifying. Hit that at the higher power level and you will definitely feel and absorb more nic than with the K3 without increasing the level in your ejuice. Actually they recommend to lower the nic when using the sub-ohm tanks.
Also be sure to increase the amounts of liquid you drink. vaping dries out the mouth, nose and throat membranes and you don't want to de-hydrate.
Good luck.

About the nic level. Once you receive you aspire K4, is it a kit with a tank? I noticed some vendors include the Aspire Cleito as an Sub-Ohm tank. That particular sub-ohm tank with your 12mg should be quite satisifying. Hit that at the higher power level and you will definitely feel and absorb more nic than with the K3 without increasing the level in your ejuice. Actually they recommend to lower the nic when using the sub-ohm tanks.
Also be sure to increase the amounts of liquid you drink. vaping dries out the mouth, nose and throat membranes and you don't want to de-hydrate.
Good luck.