I have never noticed that escorts make any difference: convoys are sunk anyway. So I usually do what you have suggested, too. Depending on which country I play, I order a few or a few more serial convoy builds at the very start in January 36. Especially as UK, Jap and US, there is a huge need of them, both because many are sunk and because a lot of new supply lines need to be 'manned' as the war goes on. As a minor axis member, the need for convoys (trade agreements) should be kept to the bare minimum, as there is no possibility to counter the RN in the North Atlantic, the Med or the Indian Ocean.