If you have the Maxwell plugin, working with proxies is the way to go. Its also very simple. Nothing complicated, just place a component that is linked to a .mxs proxy. See the manual of the plugin.
I have done much larger files with proxies, impossible to do any other way.
I could render 50 trees (700 Mb each) without much problems sraight from Sketchup. In Sketechup the trees represent just a simple volume.
The way we work now is to use Sketchup as a placement tool for Maxwell proxies. The SU files are very responsive and easy to work with. No matter how complicated.
What you do is model in Sketchup parts of your model and export those parts to .mxs You can assemble those parts later on in SU.
You can put textures on your model parts either in Sketchup or Maxwell Studio. But we never use many materials in one Sketchup masterfile since this slows down Sketchup a lot. After we done the parts and have set up the .mxs proxy we delete the materials in Sketchup since they are no longer needed for these parts. That is one of the great advantages. Very small SU files.
I have done office interiors with flowers, tables, seats etc that could never have been done in a single SU file unless these files would have grown into +Gigabytes monsters. Have a look here,
http://sketchucation.com/forums/viewtopic.php?f=80&t=52418
Proxies is how we work these days and how everybody will work in the future (with SU).
Francois