Question about Tacx Flow Smart

no accessories are needed. communication with the pc/mobile phone is via bluetooth.
depending on the bike, you may need adapters, e.g. for thru axles.
of course, you can record additional data via ant+. but in my opinion, a pulse watch is sufficient for this. unless you want to have all the data in the same portal. the primary purpose of the pedal sensor is to measure power. this and the speed are measured via the roller.

As far as I know, you don't need cadence or speed sensors. Have a look here...
https://www.garmin.com/de-DE garmin-technology/tacx/working-principle/