The installation process of an MSI only makes installation changes to the target system during the Execute Deferred sequence, so that is where your custom actions should ideally be sequenced, and as near as possible to the InstallFiles action, which is the action that installs files in the MSI.
You should condition your Wisescript actions with the "NOT Installed" condition and you should also provide an "uninstall" custom action which removes the files installed by your wisescript(s), and condition this action with the REMOVE="ALL" condition.

8000 files is not actually that many compared to some projects I've seen, so is there a reason why you have chosen to handle some of the installation via Wisescripts? 

Hi EdT
Thank you for replay.
 I install some files using wisescript because it takes too long to compile or when I make some changes to the installation then, it takes a long time to go from one page to another.
Did you have any expirience with cab files? can I use for this purpose cab files from Installation Expert -> Media page?

thank you.

While you are still making changes to the install, why not set your compilation options to "External uncompressed" files. That will avoid the long compile process while all the files are compressed into CABS. Once your install is working correctly, just change the compile process to what you need for the final release.