Render that epic scene without running out of RAM or lagging your system with what you have now.
Nothing beats a good hardware upgrade for that huge rendering job, the problem is not everyone has a disposable cash flow for that new nitrogen cooled mobo, dual hexcore cpu, a huge psu to push the triple sli cards and the 32GB of low latency DDR RAM that's going to solve all your problems, but there are several simple work methods you can do with what you have now to make bigger and more complex scenes without hitting the limitations of your current rig and they are either free or already part of Daz Studio. Just keep in mind not all of these practices work well with close up/detail and may requires some trail and error but for work on epic scenes, or crowded scenes or just background scenery these are life savers, and they work in DS3 and DS4.
• Optimize your render settings for the scene your rendering, more is almost always not better when it comes to 3Delights default settings in Studio. For example Turing up raytracing is not necessarily going to make a better render it's going to make the same render slower and more likely to crash and burn, try turning it down. There is an excellent response on this subject by Adamr001 here
• Use smaller textures, especially on non-closeup work: Do your eyeballs need to be 4000x4000 virtually loss-less jpeg when 768x768 will do and use 1/5 the time to convert to TDL during the pre render setup 3delight or conversion over to Luxrender if you use Reality? Lowering texture resolution requires less RAM to work in the scene, less RAM to render and creates a smaller (collective) file size. More often than not with this method you can not tell the difference between the high and low res textures once they're rendered. While the software to do this might have you looking at Photoshop ($$$) try GIMP, it's free and very powerful.
just don't delete those original high-res files!
• Use fewer textures when possible and supplement colors with by changing the surface of color. Green pants, blue skirt, light skin, dark skin? Use a solid white texture (or no texture) and change the surface colors to whatever you want. Use a skin texture on one M4 and adjust the surface color to something other than white, use another M4 use the same skin texture. You've now made two models with color differences and used half the textures you might have had to load/save and convert when rendering.
• Use Texture atlas (free from Daz3D at the time of this writing) and export models as OBJ's especially for distant models. Using this combo you can make a library of low polly, limited texture using scenes that load and save faster, and use far fewer resources when rendering. Keep in mind these will become static props (you wont be able to pose them, but you can position them and use them over and over in different scenes) This method does not translate well to close up work, but for crowded scenes it is infinitely better than piling up models and textures that will adversely affect load/save/file/ram use/rendering stability/interface stability. Need two people in a helicopter? I did this and got my load time down from 32 seconds to 2, files size down from 17.1MB to 231K, textures down from 80 to 1. At a glance I could not tell you the difference between the raw studio model and the one I did using the method.
Hide anything that doesn't show when you export your obj, it will make a smaller file that uses even less resources. There may be a little trial and error with this one but this is a awesome combo if you have limited RAM or several dozen gigs of it.
Texture Atlas: http://www.daz3d.com/shop/texture-atlas-for-daz-studio/
I might need to elaborate on this technique, but I use it constantly
• Discard what you don't need: As a rule, if you don't see it, get rid of it. If a model is out of the cameras range delete it from the scene. You can always make multiple scenes and save them and go back later to reposition lights, cameras and scenery. Hide anything in the scene tab that you don't need to show if you don't want to delete it.
[edited for spelling and formatting]