Ok, I'm planning a scene where one character wearing dforce clothing is sitting on a couch, while another with dforce hair is laying on the couch, using the first character's lap as a pillow. My question is should I try the dforce sims in one go, or do multiple steps?
It's preferable to work in "layers" since dForce can be finicky and crash a lot. How you work in layers depends on the scene. You will also want to get in the habit of using the animation timeline, NOT the included "render from memorized pose" feature.
A good rule for dForce is to set your timeline to 51 frames, place all objects & characters in the scene at frame 0, put them in their starting pose at frame 0 and their final pose at frame 30. This allows you to manually adjust the transitions between frames 0-30 to fix weird or unwanted behavior. Simulate the entire animation range for most scenes, then cycle through frames 30-50 until you find the one you want to render with. This is a HUGE help if the pose causes dForce clothing to do "inside" something that you need it to interact with since you can MOVE the model using this technique, starting from a memorized pose uses the character's final position as the position for the memorized pose. A simple pose like lying down can be the starting pose with the character simply raised off the surface for the simulation start to get their clothing to drape how you want it.
This gives you the ability to do cool "tricks" to get around some of the inherent problems with dForce. For example... underwear. For this you can set the underwear's scale to 50-75% in frame 0 and 100% in frame 30, this will cause the underwear to "expand" beneath the dForce clothing, pushing it out and eliminating poke-through you get when hiding the underwear from the simulation and dForce clothes "sticking" to the underwear when you don't hide it from the simulation. You can do similar things with the scenery, accessories, footwear, etc... be creative
Another key with dForce is to ALWAYS "hide" complex objects from the simulation that aren't needed (display settings for individual objects, turn "visible in simulation" off). Especially things like fibermesh eyebrows, eye lashes, jewelry and hair. You can also hide all scene objects that the simulation doesn't need to interact with. In your example, the walls, floor, lights... everything except the couch really can likely be hidden from the simulation without affecting the results. I like to leave them visible so I can see which parts of the final simulation are visible to the camera since many unwanted effects probably won't be seen in the final render therefore you don't need to waste your time fixing them. This also help me spot items that probably should be used in the dForce simulation that I had previously hidden.
To simulate in layers you have to think about what will interact with other simulated objects. For example consider the case of a dForce dress worn beneath a dForce jacket. Simulating both at the same time can get messy or cause one or both to "explode" when the simulation fails. To solve this you simulate the dress first with the jacket hidden and then go into the dress object properties and freeze the simulation (don't hide it). Then, adjust the jacket as needed to be entirely "outside" the dress and simulate the jacket. Rinse and repeat.
As your simulation gets more complex the simulation time and chance of failure increase dramatically, keep that in mind and try to keep it as simple as possible. Also, don't be afraid to cheat and use simple primitives for the simulation. A simple plane primitive placed, scaled and textured properly will look the same as a more complicated skirt with a fraction of the hassle.
Hope that helps. We could start a whole thread just to "Daz3d - Show us your dForce skills" really