A Mac uses macOS, not iOS. The latter is for Apple's mobile devices, such as the iPhone and iPad.
Office 2008 is ancient. That you get it run at all on a 2 year old Mac is a bit amazing. Though not even slightly surprising that it constantly crashes. Office 2011 is also obsolete. MS stopped supporting it almost a year ago, and it too does not run well in High Sierra, or at all in Mojave.
You need to purchase a new version. Current is either the subscription Office 365, or the one-time cost perpetual license Office 2019.
If you're using Entourage in Office 2008, that's going to be your biggest problem. You cannot import your email data into Outlook from Office 2008. It must first be imported to Office 2011, and then from there imported to Office 365, 2019 or 2016.