Base from this data: https://coinmarketcap.com/exchanges/poloniex/

They are having a $642M of 24-hour volume. I don't know if that's the average but I think this data is from their most recent 24 hours tracking.

And base from coingecko: https://www.coingecko.com/en/exchanges/poloniex

It's not that far with the data that coinmarketcap is telling as with them, it's $654M.

They do.

Check their listing page: https://support.poloniex.com/hc/en-us/sections/360006455214-New-Coin-Listings