Wordpress site database restoration and updating

Established Wordpress multisite needs fixing. Main site feature is a forum section using the Simple Press Wordpress plugin. A few days ago, I suddenly discovered more than 800 members' accounts on my site were deleted from the root site. As a result, the affected members appear as "Guest" in the forum, and not the usual "Member" status, in their forum posts. I have tried adding a few back manually via Add User (from a subsite where the member's record still exists) but the link to the forum appears to be broken, as the status still remains as "Guest" in their forum posts. I need a solution where all the deleted members are restored again and their forum status are also correctly restored. I have a full site backup dated 17 May 2014, two months old. I want to restore the site to the current state with as little data loss as possible. If I restore the site back using the backup, is it possible to import in the forum and blog posts from the past two months since that May 17 backup? If this is possible, then I need someone to do this for me as soon as possible. I need the selected freelancer to document for me the work done on the site and to also show me how the importing of forum data is done, in case I need to do further on this later. For someone experienced with Wordpress and MySql, I think this should be an easy job, so no ridiculous quotes please. I have a very low budget, but the selected freelancer can look forward to good feedback and further work if the work can be done to my satisfaction. Thank you for looking at my project. I look forward to receiving your bid and discussing my project with you soon.