Welcome! What you describe is definitely doable. In fact it’s even doable without smartthings, so it just depends on the exact options that you want. 
Lutron Serena shades will work with Alexa as long as you have the Lutron SmartBridge, which would be required for SmartThings integration anyway. So that is definitely one option and is very straightforward. The Lutron devices will also work with HomeKit if you have an Apple iOS device.
Somfy gets a little more complicated. You can get custom shade/lines using the Somfy motor which would work with smartthings, and then use the Alexa/smartthings integration. Zebra blinds is one distributor and they are very active in this forum if you have any questions. This choice may be a little less expensive then the Lutron Serena shades depending on the exact options you choose. However, they don’t work with HomeKit. But they will work with SmartThings.
Both are good choices, so I would recommend doing further research into both.
BTW, If you do have an iOS device, you can do everything just with HomeKit plus Alexa because both the ecobee and Lutron have their own Alexa integration. But you do need to have an iPad to use as the hub so you can set up your time schedules. So that gives you two methods of controlling things, both Alexa and Siri. We use both at my house. Alexa is better for voice recognition, so we use that for choice, but I do use Siri on my Apple Watch for some things. So as always different things work for different people.
(BTW, I’ve moved your thread to “projects” so you can get individualized responses based on your own needs and preferences.)