People who ride MTBs on the road usually swap the knobblies for a slick. 1.5" wide ones are the size of choice, they are fast, efficient and comfortable. You dont need a whole lot of suspension with this size tyre.
When it comes to saddles, the choice is very personal, we all have a different rear end configuration. Dont be mislead by soft squishy saddles, they may feel comfy in the shop, but they distribute weight where it is not meant to be supported. You have 2 sit-bones, which should carry the weight. Brooks make some lovely leather saddles which users swear by. They make heavy-duty wide ones as well as the narrower racing style.