Steps to Upgrade from SP 2010 to SP 2013: Make the site in SP 2010 readonly. Using SQL Management Studio, perform the backup of Content database and service database in SP 2010. Restore the databases in SP 2013 SQL server. Attach the content database to a site collection in SP 2013. Similarly, attach the service databse to the corresponding service in SP 2013. For more info please refer:
SharePoint 2010 workflows are supported in SP 2013 also. The only issue I faced while doing migration of SP 2010 site having workflows was about workflow activities:
The type or namespace name 'AssemblyName' could not be found (are you
missing a using directive or an assembly reference?)". at
association, SPWeb web) at
association, Boolean fallback) at
host, SPWorkflow workflow, Collection`1 events, TimeSpan timeOut)
Opening the workflows associated with these lists from SharePoint
Designer resulted in the error: Could not deserialize object. The type
could not be resolved.
Resolution: Web.config files needs to be modified. For SharePoint 2010 custom activities to work in SharePoint 2013, the “authorizedType” node needs to be defined in a new sub-section “targetFx” under the “authorizedTypes” section.
I also had plenty of event recievers and they all worked very well.