Test, test, test.  You are essentailly creating a very unique, niche piece of software.  More than 80% of software development is 'killing bugs'. Below is an very abbreviated list of items that should cause pause:
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Employee Benefit Statements: Pause when:
1) Someone suggests "We can do this whole thing with a spreadsheet and Word!"- If you try, we suggest you begin to dust off your curriculum vitae.2) Multiple formats for keyfields.  If you use SSN's and you see '000-12-3456' on one table and '123456' on another table, you are about to have a problem.3) You notice that an employee is missing from a census.  If one is missing ...4) You see different deduction amounts for the same benefit & ee classification.5) Someone shows as having a benefit that should not (or vice versa).6) A Table that should have only 1 row per employee has > 1.7) Wage data 'seems low' for certain people.  Check for multiple pay sources.8) A PT employee has an FT deduction for health (other) or vice versa.
A complete list could be quite extensive; as minor as typos but as major as mismatched data.  If you ever get the notion that data has not been JOINED (matched) properly, stop and evaluate before you proceed.  Don't be ashamed to ask your IT/DBA to take a look.  Their SQL experience is likely much deeper than your own.
Employee Benefit Statements: Miscellaneous:
1) Avoid 'fancy' covers in first year.  Covers, binding and offset printing can add another difficult variable.  You'll have enough challenges and won't need yet another.2) Use one-pass printing, ideally from your own location and physically located in HR.Aligning 'pre printed' images with variable, laser printed text is not dependable. (also, security)3) Do not, under any circumstance, put an SSN anywhere on an employee benefit statement. (security)4) Avoid adding other personalized materials for collation with the employee benefit statement. (human error - collating).5) Do not pass off folding, stuffing or other tasks to the mailroom or temps. Keep it in HR.6) Always remember to delete terminated employees prior to print.7) Always have a disclaimer that has at an absolute minimum, words to the effect of: "This is NOT a legal document.  When in conflict with legal documents, the legal documents prevail."8) Do not be pushed to hit an arbitary deadline.  Be calm and methodical.9) Preliminary Group meetings can be helpful by using a sample (John/Jane Doe). Don't be ashamed to tell employees it is the "first effort" and they should not panic if there is an error. Consider a prior 'Train the Trainer' session with Department heads.10) Do not distribute the actual personalized statements at a Group Meeting.  Very bad idea.11) Be prepared for phone calls.  Have notes and files readily available. Be prepared for 'lost /I didn't get my statement'.12) Take copious notes during the entire process.  The process does not end.13) If you get in over your head, stop the Project & get professional help.  If that is not an option, then abort.
 Do not depend on 'good luck'.  Rely on a methodical approach, many eyes and attention to detail.
 DIY Tutorial 10: Getting Started Employee Benefit Statements (Common errors)
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