You have successfully separated the doorbell press-button from the heavy current loads required by the doorbell ringer. That should considerably lengthen its useful life. The heavy duty wiring going to the front door will now have an extremely light load, needing just enough current to toggle the relay coil, a good thing.
The AC current to the doorbell is now switched by the relay, a relatively cheap device that can be changed over by simply unplugging it and putting in a new device. The relay contacts take the brunt of the heavy load of the current that used to be taken by the doorbell press-button, and are suitably rated (250Volts at 10Amps) to do that for many thousands of presses.
Putting a resistor in series with the doorbell ringer just reduces the current flowing to it, something you may not wish to happen for it to work well. The resistor current drop is converted into heat, and has no benefit. Your AC current now flows from the transformer via the relay, direct to the doorbell where it needs all the current and voltage to make it chime so wonderfully, and fulfil its role in life to let the person at the front door know with audible feedback that they do not need to keep endlessly pressing the button. The doorbell transformer may have a built-in fuse if it is shorted, or you may wish to have a slow-blow fuse or resettable low voltage circuit breaker in line with the bell rated for something like 2 amps for the unlikely even the door-bell chime mechanism stops in a ‘shorted contacts’ position.
The additional current taken by the relay and Shelley are relatively minuscule, and (if using the 12V connection for them and the 8V for the bell) well within the capabilities of the transformer you are currently using. The only added current load is continuous for the Shelley unit, and is less than 1 watt. In the future, should you need to replace the transformer, get one with just one 12V AC secondary at 2A rating and you will have plenty of excess capability for longevity and cool operation, and it will work well with the existing wiring, relay, Shelley, door-press button, and chime unit, all unchanged.
I have suggested you wire the relay directly in circuit with the door-bell push-button, rather than go to the Shelley Uni inputs and then activate the relay via automation, as the delays for this to be processed may be unacceptable, and not provide direct feedback to any persistent button pusher at the front doorbell. As it currently stands, when you press the button, the relay activates immediately and the doorbell rings. This means your suggestion that you might be able to isolate the ringer at undesirable hours may not be able to be achieved, however have you considered what would happen if somebody needed to interrupt you at inconvenient hours for safety reasons such as to let you know about fire and theft of your car outside?
I note that there is mains power at the top of your front door going to the outside light. Maybe you can tap into that to power any devices that are going to be used for video input and audio output, etc. My previous comments about wireless connection loads being heavy for a video feed still apply.
Looking at the bigger picture, you have repaired your doorbell, and have made it robust, as well as reliable. Expect many decades of reliable service.
You also have acquired the doorbell press-button activity into automation, local and/or cloud based. This was your primary need. This has been achieved without major rewiring or large cost.
There are many options for cameras, messaging, alerts, recording, presence sensing, remote door unlocking, NFC or fingerprint presence detection, and even voice assist to explore, now that you have captured this event.
How you use that is now up to you - the world is your oyster!