Can all custom features and data from our open-source version be fully replicated onto a new CRM platform?

To move from an on-premise to a cloud-based solution, you would have to pick all the data from the existing system and place it safely and securely in the new one without losing data integrity in transit. 
This process of migrating data from an on-premise to a cloud-based solution is called Data migration. To perform data migration, you will require an external migration tool or an intermediate service. Vtiger recommends the Move2Cloud service for transferring data from Vtiger Open source to the Vtiger cloud edition.