Hello everyone! Looking for some expertise in setting up a new business unit in muilti org Salesforce Marketing Cloud and connecting with SFDC data. 

We just established a mutil org in marketing cloud. My company was just acquired, and we are now running a pilot test with our "Mothership" to market ONE of their products via our marketing cloud technology. We are trying to connect our new business until to the "Mothership" instance of Salesforce. The "Mothership" instance of SF has around 1million contacts (their instance is a little messy – with dups , unmailable contacts , etc.) and we are only marketing to around 10% of that population. To help segment this small audience, we plan to add these contacts to Salesforce Campaigns and use those campaigns as our entry events in journeys. If we go this route, is there any need to synchronize our data in the Contact Builder? Our issue is that we do not want to synchronize 1M contacts (use our mkt cloud storage) when only a small portion of that population actually applies to this pilot test. We are able to pull over all the data and fields we need on the campaign level in our entry event of the journey.

Could this solution work? Or do we still need to synchronize our SFDC data on the contact object and campaign object.