A couple of cross blog references here on resource management topics – and both affect Project Online as well as the on premise installations.
Firstly an issue where you cannot open more than a certain number of resources from your Resource Center in Project Professional 2013 – blogged over on the Project Support blog at http://blogs.technet.com/b/projectsupport/archive/2013/03/11/project-server-2013-why-can-t-i-open-all-my-resources-from-the-resource-center.aspx. The numbers aren’t exact – but will be around 120 for IE9, then 520 or so for IE10, Chrome and Firefox. (This functionality doesn’t work at all in Sarafi on the PC, and obviously wouldn’t on the Mac).
The second one is from our very good friend Gary Chefetz over at MSProjectExperts and unlocks the key to the Windows Logon Account field if you wish to add resources via Project Professional 2013 - http://www.projectserverhelp.com/Lists/Posts/Post.aspx?ID=205 . Also note Gary’s comment on needing to select at least one resource from the existing resource center to open Pro up.