Account Contact Relationship Object

Hey Everyone,

I'm looking into junction tables and custom objects to relate contacts to multiple accounts in Marketo. I've found a few posts around the community (thanks @grégoire_miche2 and @sanfordwhiteman), but want to ask a few clarifying questions.

1. It looks like Marketo stores all account records in the database, even if no leads/contacts are associated to that account. I pulled a report in Salesforce of accounts without contacts AND without related contacts. I am able to see those company names in smart lists pre-population when I try to filter for them, it's just the list returns no records in Marketo (since no people records are tied to them). Does this mean that the account table, even for accounts without contacts or related contacts is already built? Including all of the fields on that record in Salesforce?
2. If the answer to 1 is "yes", then wouldn't it mean I just need a junction table that ties Salesforce ContactId and AccountId to add the relationship? Would that allow me to then segment contacts based on those account relationships based on all the data Marketo has on each account record?
3. If the answer to 1 or 2 is "no", do I then need to create a junction object and a related accounts custom object with all of the fields I need (probably don't need every field from SFDC)? Or would it be best to just use a single custom object and skip the many-to-many concept in Marketo?

Thanks in advance for any advice.

-Sam