If I file for a 402 reduction now (1year after completing probation) will I still qualify to have it expunged after 5 years?

A 402 reduction will not make it harder for you to have any charges expunged. Depending on your specific situation, it could make it easier. From your question, it is not clear if you are eligible for an expungement. You listed four (4) different charges, but did not say if they were from the same criminal episode and which specifically are drug charges. I would also need to know what level of misdemeanor the three (3) misdemeanors were. Talk to a criminal attorney about your complete history.

There wouldn't be a down side to a reduction, it could only help. But the previous answer is correct in that you may or may not be eligible. Talk to criminal defense attorney to review your background and determine whether or not you are eligible.