As you plan your migration from your on-prem SharePoint farm to SharePoint online, I would like to encourage you to look at the SharePoint Migration Tool being released by Microsoft. The tool was made generally available 1/9/2018.
First we recommend the following hardware for the on-prem tool machine that is performing the migration, this will insure the optimal speed:
CPU: 64-bit Quad core processor or better
RAM: 16 GB
Local Storage: Solid state disk: 150 GB free space
Network card: 1 Gbps
Operating system: Windows Server 2012 R2 or Windows 10 client
.NET Framework: 4.6.2
The tool was designed to move items from a document library on-prem to document library in SPO, for authentication you need to have read on the source and Site Collection administrator on target. See this article for more information about how the tool works.
You can run bulk migrations by using a formatted CSV file, see this article for specific information on the formatting of the CSV file.
The tool will maintain permissions from on-prem site to SPO site, if the user already exists, the easiest way to insure this is to setup DirSync. If this is not possible or you have specific needs then you can customize a user mapping file by following this article.
Of course we have Advanced settings like Enable Incremental migration, Migrate File version history, Do not migrate files created before, and others that you can use to tailor your migration. Please read here for descriptions of these settings.
Finally you can download the tool here.