Thank you for your question.
Please permit me to assist you this morning.
If you choose to elect your benefits early, then the benefits you receive for life would be locked in at the lower rate.
Plus, the benefits you would receive still be subject to the annual income limit for outside earnings.
The current income limit is $15,120. Here is the link to the information: http://www.ssa.gov/policy/docs/quickfacts/prog_highlights/index.html
In terms of back-taxes, it would not reduce your benefit BUT your social security payments could be intercepted and garnished for payment. It would reduce the amount you receive, but not the actual benefit you are entitled to.
If you continue working, you would continue paying into social security even if you own benefit would no longer increase once you elect to take it.