CoinPayments is not used in the plugin as an exchange rates provider but as a wallet, via a coin adapter.
Exchange rates are pulled from other sources, but these are not historical. These are current exchange rates that are used to do calculations.
Your exchange is currently empty and it cannot “borrow” liquidity from another one. This plugin is an exchange itself, not a frontend to a remote exchange. So, unfortunately, what you are proposing is not possible.
The same is true for the bids/asks table: You can enter any bids or asks you want. In theory, as your exchange grows, there will be price discovery, and prices should converge to whatever the market value is for a coin, due to the actions of people performing arbitrage.
Hope this is a bit clearer.
kind regards