Also: if I'm adding a field to a Custom Object that is not currently a custom field in Marketo, how do I go about capturing that info in a list? (such as "Accomodations needed" for an event)
There’s no inherent connection between Person-level custom fields and CO-level custom fields. That wouldn’t make sense, it’s one-to-one vs. one-to-many!
The only way you can simulate a connection is by using a Smart Campaign to read a field from one of the person’s CO records and write a corresponding field on the Person. Although as noted above, you can’t simply Change Data Value to a token, you need to have choices (“if a CO record exists with Field A⩵ABCDEF and Field B⩵123456, then set person Field C=123456”). In general, there’s something wrong with your architecture if you’re putting together lots of campaigns like this.