​It is technically possible to add the same account as a Master and as a Slave at the same time. However, to do so you need 2 distinct Trade Copier cockpits (2 distinct usernames). When you will try to add the second account it is possible that you get the Account Already Registered error.. In that case, we just need to manually allow your second account. Please just ask if it happens.

Can I manually close trades from the Cockpit?

Yes, you can close trades from the Cockpit. Only Slave trades can be closed from the Cockpit, not Master's trades.