Three TV's on one account with 3 4K Sticks?

Each Roku has a single HDMI output that must be connected to an HDMI input port on the TV to which it is to be used.  So yes, you'll need a Roku for each TV.

Your channels and subscriptions reside on your Roku account.  Each Roku linked to that same account has access to the same channels and subscriptions .  Add/delete on one Roku, add/delete on all Rokus linked to that account.  There are no additional fees for using more than one Roku on the same account. 

Considerations:

• Some paid subscription channels may limit the number of simultaneous streams they will support on a single account.
• Paid subscriptions made through a third party like Roku, Amazon, Google, etc. typically can only be accessed through that same third party, linked to the same user account on that service through which the subscription was made.  For maximum flexibility to view on multiple platforms (computer, streaming device, smart tv, phone, tablet, etc.) subscribe to the channel provider (Netflix, Prime, Disney, Paramount+, etc), directly on its website website, rather than through a third party.
• If you want to have a different selection of channels on different TVs, each channel combination will require its own Roku account, identified with a unique email address.