Hi Amanda,
As per integration, there is a really good and detailed technical manual on how to setup events Marketo + GTM, please find it here: http://pages2.marketo.com/rs/marketob2/images/Marketo_GoToWebinar_Adapter_UserGuide.pdf.
As you'll see in the manual, you have the option of using a Marketo or non-Marketo landing page for event, but the Registration form on the landing page must use a Marketo form to register your leads for the event or non-Marketo form with API integration to push lead registration data to Marketo. We always set it up with Marketo form hosted on Marketo page which we then include as iFrame on our web page.
I always send confirmation (with webinar URL token), reminder and follow up emails through Marketo and therefor I always disable all GTM email notifications. But if you won't be sending these emails through Marketo, you can leave them in GTM.
Hope this helps...