I find that anytime I am working with a large scene, it is easier to split it up into parts then it is to have it all loaded at the same time.
In this case having the forest as its own scene and each fully dressed character as their own individual scene.
If you need to place and pose a character after you built your forest then you would load the forest in after the character and then remove all that you do not need. So you would end up with the forest floor and maybe a few trees in the scene with the character and then when the pose and placement is complete, remove anything not related to the character and save the scene.
What this does in the end is it makes dealing with each character or element faster and thus easier since the load and save times will be a lot faster and of course your computer can handle what your doing a lot better too. Also if you need to go back and make a minor tweak on one character you dont have to load everything else too.
When it comes time to render, just load the first one and merge the rest. Just make sure you save your desired camera angle in one of the scenes too along with your lighting!