To shed some light on pricing. You do not get a portal with your marketing license - rather you get 1 subscription management marketing page that is hosted by a portal/MS.
"You can choose to run your marketing pages, landing pages, and events website either on an external web server (such as your own CMS system) or on a Dynamics 365 Portal or Power Apps Portal running on the same tenant as your Dynamics 365 Marketing instance. Dynamics 365 Portals and Power Apps Portals are licensed separately from Dynamics 365 Marketing." https://docs.microsoft.com/en-us/dynamics365/marketing/purchase-setup#how-marketing-is-licensed
There are different strategies to how you can manage the different kind of events – are they online (webinars) or in-person? For webinars, there are integrations OOTB that will push your registration information. For in-person, you would need the event portal (just a type of MS portal). Note: the portal is not included with your licenses, this is an additional cost (or MS would say optional add-on - https://docs.microsoft.com/en-us/dynamics365/marketing/portal-optional#how-portal-integration-affects-marketing-features.) What makes the portal ideal is that you are able to expose Dynamics data out to the public or require a sign in to see the data; this can be event data or any entity. If sign-in required you are also able to allow this individual to update specified information that is in the CRM (i.e. contact information, their flight/travel information, etc)
We have implemented Microsoft Marketing for a number of clients that both use and don't use events. I can show you some samples. We implemented Team Rubicon's Dynamics, Marketing, portal, etc - https://www.youtube.com/watch?v=_W6j-Lzdq_c . They use events for scheduling out all of their volunteers for single day and multi-day/month events.
As far as success? Absolutely, if it's not out of the box, it can be customized.
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