If I upload new contacts to my List and that List triggers a flow, will those contacts be scheduled to receive the flow messages?
Yes. If you would like to ensure that these customers are not queued to receive these flow messages, set the flow to Manual or Draft before you upload your contacts to the List. If you set the first message in the flow to Manual, these profiles will queue for the flow messages but will enter the "Needs Review" folder. Once all profiles have queued and entered "Needs Review," click into "Needs Review" and select "Cancel All" to remove those profiles from the flow. You can then set the flow once again to Live.