You will probably get the same issue with most any device. Your questions are not device specific, but are for streaming in general and would affect any device.
Roku is a DEVICE, not a service. Technically, NOTHING is included. You install the apps/channels you want. There is NO COST to using the Roku itself. Any costs would be for paid subscription services.
"Free subscription" doesn't make much sense. There are many free services out there (often called FAST channels, for Free Ad Supported Television), and you can create accounts to allow device portability (same setup on multiple devices.)
As far as ads on subscriptions, it depends. Most of the big name ones (Netflix, Disney+, Max, etc...) have ad-supported and ad-free tiers.
Lastly, if you do want to use a paid service, I STRONGLY recommend not paying through Roku. You can go to that services WEB SITE and sign up there. When you install the app on the Roku, you log in using whatever credentials were used to sign up on the web site. Doing it this way removes any middle-man for payment issues, and usually allows you to use it on most any device. Paying through Roku sometimes means it will only work on a Roku.
