If you haven't already, I'd recommend you read the Keystone SolarFlex Quick Start Guide at:
https://keystone-rv-dealer-app.cdn.p...DF_QSG_WEB.pdf
On about page 15 is a question: Why can't I build out my SolarFlex 200 to be like the SolarFlex 400i ?
In Keystone's answer to that question you'll find their explanation to some of your limitations. They also provide a recommendation in that paragraph which will take you back to the SolarFlex 200 information page where you'll find an "expand your system" section where you'll find a list of factory recommended "upgrade options".
I'd start there, and then start weighing the "user recommendations" to supplement what the factory provides and their upgrade components.