to remove the nav bar-
decompile either framework-res, or system.ui depends on your rom.
once decompiled go into Res->Values->dimens.xml
for the rom im on its line 14, 15, and 16. replace the x.x dips to 0.0dips to remove the navi bar completely.
save the .xml and then recompile framework-res or system.ui and replace your current one with the new apk
if your going to do this make sure your using lmt, or some type of other way to use home, and back, etc
the lines your changing should say