From Dr. Kiernan's book: Acid phosphatase survives brief fixation in cold aceton or aequous formaldehyde. ...Frozen or cryostat sections retain the greatest amount of enzymatic activity, but .. will work ...even on paraffin sections if a wax with a low melting point has been used.
He doesn't recommend a special thickness, therefore I think the usual 3-5 µm will be ok.
Reading this, I think the processing of your tissue will give you perhaps more problems than the section-thickness.