Hi there WWW should have no effect unless the cache is specific to that URL and it's trying to pull the cache which doesn't exist, and where it processes it, it caused the internal error. Or maybe your site is not configured for WWW but you're trying to access it through WWW in which the cache got mixed up? You can still use the cache plugin but you must properly configure it, and make sure to exclude theme assets from minification.
As for the Typekit, yes, it usually happens when you activate it and didn't add proper Typekit ID, which means it's pulling some 404 resources from Typekit server. And you don't need Typekit plugin, you can utilize the theme's Typekit feature.
X/Pro > Launch > Options > Templates > Fonts And click the
T icon, then go to Typekit Section and add your ID.