There's no reason to heat the honey. Doing so is likely to remove some of the flavor and aroma, though just how much is a point of contention amongst meadmakers and the like. Honey is one of the few organic products that will never go bad (provided it doesn't separate), so there's no real risk of infection from the honey itself. The lid of the jar you're keeping it in and such is another matter entirely, but the risk is still low (as your fermented beer is already very inhospitable to most bugs).
If you do add it to the secondary, make sure to mix it in well. If you just pour the honey in, it's going to sink to the bottom with the trub and sit there. You might consider adding some water to the honey initially, mixing that well, and then adding to the fermentor; it will be much easier to mix in that way. With a beer this light, you might get some honey flavor out of a 20% recipe amount. Just find a good quality honey with a big flavor and aroma. Don't expect preheated el cheapo grocery honey out of a bear shaped squeeze bottle to taste/smell terribly good. It won't.