Is this backpacking journey safe for a couple?

Hi, I'm from Ireland and my girlfriend and I are planning to do a backpacking trip through Central America. We will be flying from Ireland to Miami, spending a few days in Miami before we get a flight over to Cancun from Cancun we will be traveling down the coast to Belize then Honduras, Nicaragua, Costa Rica then we will be making are way back up through Nicaragua, El Salvador and Guatemala through Mexico again to get our return flight from Cancun back to Miami and then from Miami back to Ireland. Now our trip is going to be 8 weeks and I was wondering if this route is very dangerous? And what is the state of Mexico like in the south?