The above is why we tell first year students to keep the number of classes low the first semester. It's better to take fewer credits and do well than the opposite. You cannot believe how difficult it is to bring a GPA up if you blow it the first semester.
12-14 credits is PLENTY to take your first semester. A lot of time and energy goes into adjusting to college your first year; it kinda sneaks up on you. Allow for that in the fall semester. As an upper class student you will do well with 18 credits. Just not at first.