Devil's pie enable to open the application in a particular workspace.

[Install]

following command:

sudo apt-get install devilspie gdevilspie

gdevilspie is GUI based configure tool.

[How to use]

For example, to open firefox in the workspace 2.

mkidr ~/.devilspie

gedit firefox.ds

Following code Cut & Paste into editor,And Save.

; generated_rule firefox

(if 

 (is ( application_name ) "Firefox" )

 ( set_workspace 2 )

)

Start or Restart devilspie.(In most cases, Devilspie registers to auto-start)

Detailed usage of Devil's pie is follow links:

http://www.webupd8.org/2011/02/how-to-start-applications-minimized.html

http://www.foosel.org/linux/devilspie

http://live.gnome.org/DevilsPie

Devil's pie may be useful for your ask of Fixed width and height for new opened folder/file.

EDIT: Sorry, "Set workspace" is not working in Compiz but working in gnome-shell.

I don't use compiz here - but I think the plugin you can use to
achieve opening apps in specific windows is Place_windows or
window_rules.

Whether that will conflict with unity is something that I can't
comment on at present.

What he say is correct.

If you use Compiz in ubuntu session, you should use Place windows plugin like as following link. but Place windows plugin conflict with unity.

https://blog.so-net.ne.jp/_images/blog/_7b2/ankyo/SS-ccsm-plase-window.JPG

The above screenshot, I enable the Place Windows plugin in a special way to avoid conflicts.