The permissions are based on roles and they apply to all blogs and posts. Your approach is achievable. It is possible to get the current user based on his/her username.
For the backend - you can use UserManager.IsCurrentUserInRole method. You should map BlogsListView template and on Page Load check whether the current user is in a restricted role. If so, hide the other posts/blogs from the grid. By doing so the current user will see only his/her post in the RadGrid MasterTable.
For the frontend we use BlogPosts control. There is an option to enable posts moderation or disable the posts. You can do this from Sitefinity UI. If you want to restrict particular users you should map ListPageDetails template and subscribe for repeater ItemDataBound event . Then check the user's role, find CommentLists control and set it as enabled or disabled (cmmLst.Enabled = false;)
the Telerik team