As a melee character, I am often melted by plague, desecrator, and molten Boss Modifiers, tearing through 24k HP. What can I do to delay my death? How severely will resistances assist, and what resistance should I pair with each Modifier? Is it worth equipping resistances before entering, say, an area with many molten enemies? What about the INT stat? How much do I need to equip (as a DEX character) before I start seeing results? What other skills and buffs apply here?
The best thing to do would indeed be to stack resistances.
I'd strongly suggest finding items with a decent amount of your Primary Stats, Vitality, and Resist All Elements for melee characters. If you find yourself having more trouble with one specific type you can always look for resistance armor on the AH for that specific stat. Resistances are a huge deal in the harder difficulties for melee characters, so I'd highly suggest stacking Resist All Elements items (Rapida had to start doing that on his Barbarian in order to survive certain effects on in Inferno).