This is what I know few years back but not sure if it still applies now.
During your nsf period, the minimum you can go is lcp. This is the norm for all nsfs. Nearly all nsfs (those without any bad records) will get this lcp after 1 year of service. And they will ORD with minimium lcp.
As for cpl, you must pass your ippt during your second year of service in order to get this cpl. Your ippt must be done after you gotten your lcp status in order for you to ORD as cpl.
So basically promotion to lcp and cpl is not difficult. It is like the norm or basic standard set for all nsfs. The exception will be promotion to 3rd sgt. That one need to see a set of criterias such as performance, qualification, pes status, and selection test to determine whether you are fit and qualify to be one.