1) Since my final comp exceed the RAM I have, my idea is to pre-render every pre-comp, which so far my computer seems like it can handle. Is this a good plan?
The problem is, in one comp, even when I let it pre-render from the beginning of the comp, it moved it's place in the comp it was nested in, which didn't work. Not sure why it moved it, but basically the element I pre-rendered was no longer in place in the scene.
2) If I trim my pre-comps to the time markings that they actually contain active layers, this saves time in pre-rendering, but moves them in the final comp timeline. For some reason I can't figure out how to re-position them in the timeline, as I can never get the pre-renders to show up. Advice?
1 - If your precomp uses Collapsed Transformations, then you cannot prerender it. Collapsed Transformations rely on factors within the primary composition, such as cameras, lights, additional transformations etc, which simply won't work in a pre-rendered workflow.
2 - I don't understand the problem. If there are no active layers in the precomps when there don't need to be, the render time of those empty frames should be very minimal. Make sure all the unnecessary layers are removed or cropped within the precomps.