Does the Electron Cash wallet include the bitcoin I had in Electrum? If so how do I distinguish between the bitcoin and bitcoin cash? When I went to get a receiving address from coinbase it warned me if I send the wrong currency to it, it will be lost forever.
It doesn't. It should only show the Bitcoin Cash that is in those addresses.
Also the dates for the transactions shown in Electron cash are from 2017 not 2021 and they don't seem to correlate with the amount I sent. I sent 0.77 bitcoin cash and the balance showing is 0.00489243 BCH, which appears more like a bitcoin balance to my uneducated eye. I am certainly not aware of it but is it possible that I have put the wrong seed in and this is showing me and old wallet I did not know/remember I had with bitcoin in?
Yes. Go to Console and type in this:
ismine("ADDRESS").
If the response is false, then you have the wrong wallet. If the Console is not in the tabs, go to View and Show Console.
Another possibility which is also quite likely is that the address that you've generated is not within the gap limit. For that, just key in this into the console:
[wallet.create_new_address(False) for i in range(100)].
The command above generates 100 additional addresses. This assumes that you have generated and used at least 100 additional addresses from the 2017 to the current day. You can increase the integer as necessary.