Is it possible to import the Xert-(smart)workouts into the Tacx desktop app? I want to do these workouts with the Tacx flux smart. I can use also a Garmin 1000 edge?
“Smart” workouts must be run on the Xert mobile app or the Connect IQ app.
Easiest option is to run the Xert mobile app connected to your trainer.
Otherwise you need to install the Connect IQ app and deal with Garmin quirks. 
If you export a Smart workout to use with another platform it becomes a standard block workout. The XSS value will be similar to the original, but curvilinear or smart intervals are not supported.
No, it is not.
Yes, you can, but you should use the Xert player, as mentioned above. You will have to give the Edge control over your Flux, not the Tacx desktop app.
If you also want to move in the Tacx desktop app, you can use the BLE channel, if that’s free (the Edge will normally pick the Ant+ channel), but it must not control the trainer.
Not sure if you can use only the power coming from the Flux in the app - I’ve tried to do this a few times with my Neo, but usually it fails at some point.
At any rate, if you want to try this, first get your Edge to control the Flux, then start the TDA and deselect the Flux as trainer and pick only power and RPM…