The Power CMS is just a prebuilt content management app. When you install it on a working php server you just need to connect it to the MySQL database. When you add content it will be saved in the database. To get the content to appear on any page in your site you must ensure that it is a php type of page and you just need to add in the CMS code that is in the admin area.
You can use the Power CMS on a live site or a testing server. When it is time to transfer things over you just move the files and export the db.
You should definitely get things up an running with the redesign, then you can use Power CMS to control the content on the pages.
You can make use of Security Assist to update the security on the Power CMS pages. This will allow you to have a set of admins for manipulating the pages. You can make use of some other WebAssist tools to accomplish these other things. For the jobs listings you could just create specific job listings in Power CMS then only show them when you need to.
