Thank you for your kindly comments.
"the hero/foreground tree movement was immediately brought to my attention and seemed out of place; would a moving cloudscape reinforce the sense of moving air enough to make it not a distraction? or perhaps sound (my workstation doesn't have sound - so it may be there already in which case ignore above)"
I use only one hdr from cg-source.com and (a little desaturated) I didn't want to add a background (a sky timelapse for example) in post production process.because I think It kills all natural illumation from hdr and changes the background/foreground balance. I choosed other way like you said; sound effects... I mixed some wind, bird and water pool sounds for all scenes one by one with FL Studio/altiverb (convolution reverb plugin) for give a 3d surround feel . I think it looks good.
Chair scene is my favorite one in this project.

You're right. It looks a little creepy

Maybe a sound would solve this.like a door shutting sound.
And answer for your technical question ;
This scene have 18 million polygons after optimizing scene (moving proxy, proxy and instances) and 5 different Forest Pro objects (grass etc.). I never live a Vram or Ram or any error... Octane easily made its work...
I never use a post production technique for pannings or DOF with Octane.
Every scene rendered with native Octane's DOF, motion blur etc.No render elements, no fake things.. Everything was Octane's raw render.
In post production process I added some color correction, contrast and vignetting.
8000pixel renders are possible but I took some renders ( max. 5000 px) for advertising of project without any problems.
I must say that as an old Vray user:
Octane is very user friendly, fast and powerful render engine. But you must make some practices on it and must forget Vray, Corona, Mental Ray's slow, boring and chance based workflow.

Octane is easy as taking a photo with your camera..