• Fully decentralised history of trading data; volumes traded and inter currency rates going back over time.
• Fully decentralised history of bid/ask data; a set of the bid/ask history going back over time.
These can be tonnes of data (over time) if transactions are frequent. Will the system users pay for downloading these data? From whom? - a decentralized system of data brodcasters should be established just like a system of escrow agents.
The above is good for depth of market (DOM) analysis, but you will most importantly need:
• Live trading data (in ticks) - data of actual transactions happening is needed to plot charts.
It would be okay if the timestamping were not just in seconds. If the system is to succeed, in future you need at least milliseconds or even microseconds (for both historical and real-time events (ticks).