We've tested MultiChain with millions of assets, but not billions. As for the total amount of data, you have to consider what will actually fit on a single (logical, not necessarily physical disk drive). One billion assets with 120 MB of data each is 120 Petabytes of data which is thousands of the largest hard disks currently available. MultiChain will not be suitable for that amount of data, and you should use a storage system specifically designed for that sort of scale.