i would first reccommend reading this
Smartphone & Pocket PC Magazine Expert: Werner "Menneisyys" Ruotsalainen - Relocation tutorials/hacks
otherwise, dont use your internal storage for anything except apps that HAVE to be installed to the evice such as today plugins.
after apps are installed to internal storage or to a memory card, its ok to remove the help files associated with the app and i personally move the installer files in \windows\appmgr to external storage until i am going to install/upgrade something.
if you have a lot on your device in internal storage, i would start over. make backups of all your settings for your apps. copy or save those files to sd. hard reset, and reinstall everything you can to sd card.