There are three in DF, four in JO. Will you be doing each of the difficulty settings from DF? If so, what will you do with the fourth? Will you make it something special like Jedi Mode, God Mode, or just another difficulty setting even harder than HARD from DF?
MilesTeg and I discussed this the other day and I think the consensus was the difficulty would be increased by having less armor/health/ammo available to the player, rather than more and more enemies.
Nothing is final though yet, and we'll have to playtest the actual levels before we know for sure.
My cousin and I HATED that 50 health and no shields on the highest difficulty setting. Do as you will though, because I'll just play with Invulnerability enabled after beating it straight through Easy, Medium, and Hard.
***I think you should add enemies from JO into DF, like AT-STs and Rodians, Weequays, etc. Also rearm some troops in later levels with the repeater and mortar launcher. This is just a thought to enhance gameplay for the JO fans who have never played DF. It will also add to game difficulty.