how to have custom post template including custom write panels for the users to post

Maybe scribu‘s Front end Editor would be an easy way to update your website if your client finds the WP admin to be “confusing and difficult“.

But also bare in mind that the admin is customizable through admin themes, as well as various scripts and plugins. To cite only one plugin, try Adminimize, it will allow you to remove a lot of unnecessary stuff from the interface.