The smooth dimming is going to be almost impossible to achieve, especially being cloud based lights, but you can do dimming step by step… with workarounds. I already requested a official action for relative brightness control with buttons but looks like it’s not happening given all the years people have been asking for it:
For the scene switching you can use my virtual scene switcher, I made it for that use case. You can go scene by scene or let it auto-switch until stopped. Note that if you want to start/stop on hold/release your button must support the release event in SmartThings, otherwise I would suggest using the “Use same action for start/stop” in the settings of the switcher and just click one time so it starts and click again when you want to stop.