I do not in anyway claim to be an expert on the Islamic Empire. But Islam (today or even in the past) does not equal the early Islamic Empire.

The religion seems to have evolved considerably from the early Islamic Empire. Which is common. Every major religion seems to have undergone several major metamorphoses.

Not really, no. The Coranic prescriptions have been relatively unchanged since a thousand years. Given the combination of textual and oral traditions, and the low divergence of historic Qurans over a wide area, we can conclude that the Quran did not significantly change.

The Coranic prescriptions about usury and other economic activities are incredibly clearly written.

The only conclusion is that there is no reason to believe that it was in any way different to today, and a lot of reasons to believe the restrictions on free trade are even higher than in the modern Islamic world.