Installing extra modules requires a user account with the VCV Rack website. Once you have that you can login inside the VCV Rack application and use the Plugin Manager (the "Manage Plugins" button is located at the top of the app). It should take you to the website. On the Plugins Manager page add all the free bundles to your cart and checkout. Go back to VCV Rack and click the "Update Plugins" button.
While the ideal workflow for modular is generally to do work directly with the modules, as that makes a more intuitive way of synchronizing signals, there is a free module that takes a midi file and converts it into a piano-roll style sequencer which is saved in vcv rack's save data. https://library.vcvrack.com/squinkylabs-plug1/squinkylabs-sequencer