Creating events tied to a person record

I have a table of people, for a fundraising db, and a table of events.

Each event needs to be tied to a person, as it contains their payment info, etc. There need to be many events per person.

I want to have a layout that displays all events per person. I am planning on using a portal for this.

However, I can't create new events on that page, as they need to be looked up. I did this by creating a field on the Events table which is joined to the Person serial.

On my layout for creating an Event, how can I get that Person serial? I have a choose Person field, created by a value list that looks that the People field and references a Full Name calculation.

I suppose I need to do some calculation based on the name selected, get the person's serial from that, and insert it into the events person serial. Can someone help me with that?

I can clarify if needed.