"[M]any employers are unaware that they may also have a 5500 requirement for their health and welfare plans, possibly including health, dental, vision, life insurance, short-term and long-term disability, and health FSA plans. The rules surrounding 5500 filings for health and welfare plans ... remain somewhat confusing for most employers.... The exception for plans with fewer than 100 participants is probably the item that catches most employers off-guard.... Employers in the neighborhood of 100 participants or employees should be especially mindful of the number of participants in each applicable health and welfare plan."