Find yourself a Certified Financial Planner, they are better than an accountant. They are bound by law to look out for your best interest. I have been using one and have been very happy with the results. His management fees are very good.
Pay off the house. If things go bad, job loss, death of family member, major down turn in the economy, you will always have a place to live. There is great peace of mind knowing the bank cannot come after my house if I can't make the payments. If you invest the money and a major down turn comes...