I worked at a startup that was a financial account aggregator, and helped build the technology behind it, though we targeted a different market than Mint etc ta

I worked at a startup that was a financial account aggregator, and helped build the technology behind it, though we targeted a different market than Mint etc target. I can answer questions but it takes a hell of a lot of engineering to build something to even support 50-100 institutions. There are just tons of barriers technically. I think your best bet would be to license data from an existing provider and build out your own support as you go along.