I have one channel (Hulu I think) that I signed up for, that when I initially did it, would _not_ do the Roku billing method for whatever reason. Now it supposedly will, but I seem to be unable how to figure out how to do it.
1. Do I need to log on to the channel's web site and set it to not auto-renew ?
2. If I do that, do I also need to sign out of the channel prior to the date when it will NOT renew?
3. After it has NOT renewed - do I add the channel from the TV / device or while managing my account / subscriptions on Roku.com ?
Personally, t would keep ALL billing DIRECTLY with the services. It eliminates all sorts of headaches and problems, and gives you the maximum device flexibility. What if you decide to dump Roku for something else? It also makes it easier to watch on phone/computer/tablet as you know the correct login. Some services billed through Roku may only work on a Roku.
One issue with Roku billing may be the account used for the service. It probably uses your Roku email and password. Not sure what would happen if you were already using it.
Again, unless you must absolutely have all your subscription info in one place, I would recommend keeping things outside of Roku.
I have only gone the other way (from Roku billing to content company billing) but the process was basically like you said. Turn off/cancel auto renewal. Wait for it to run out. (Usually I'd wait "a while" after to be sure.) Make sure Roku app has reverted back to offering sign-in/sign-up options. Then establish at content company. Sometimes content company already knows you. In that case, I reset my password, and log in directly and fund the account, then sign-in on Roku.