Re: paying off the mortgage--not sure. On the one hand, 3% is a damn good rate. And the markets are, over the long term, HIGHLY likely to do a LOT better than that. That math says invest, in which case you max out those IRAs like everyone has said.
On the other hand, paying off the mortgage is a guaranteed 3% return, in the form of reduced future outflows. You can't find a guaranteed 3% these days. And while investing the funds should produce enough income to more than offset the interest, we Mustachians also know that it's often more important to reduce expenses than to increase income, right? If you invest the funds, retire before you pay off the mortgage, and then the markets take a dive, having a mortgage payment for a few years of retirement could take a much bigger bite out of your assets than you bargained for.
So personally, my thought is that it depends if anticipate living and staying at your current place when FIRE rolls around. If you plan on something else--downsizing, moving, etc.--pay the minimum and invest the difference. For my situation, I think there's a good chance I could be in my house for the long haul, so I want to have the thing paid off by the time I retire. Reduced future expenses means reduced uncertainty of being able to pay those future expenses.