For the issue you are having with power gallery, see this thread to see if it fixes the problem:
I will start a support ticket so we can look into the problem you are having with Power Store 4 and Power CMS.
See this thread for details on adding HTMLEditor 3 to PowerCMS:
for the image paths issue, I suspect that there is a problem with either the HTTP Address used on the Local Info tab of the site definition, or the URL Prefix used on the Testing server tab, what have you entered for those 2?
Also in the WebAssist/Forms/HTMLEditor/Site Settings what is the upload folder set to?
you say the file manager doesn't work, but dont explain the issue, can you please provide more details so I can help with this?
For styles, you need to Click on the pencil icon next to the Modify the options listed in the Styles Menu of the HTML Editor Toolbar, then define your styles and their settings on the next page.