You need an ANT+ USB stick and a speed/cadence sensor at a minimum. If your turbo trainer is supported this will give you a virtual power reading. Not as good as a proper power meter but still ok. You’d need an ant+ hr monitor if you wanted hr displayed, not sure if the polar is compatible.
As for fans, I’ve got one of the fifty quid screwfix floor ones, it’s very good though still struggles in this heat, just ends up blowing hot air. If you can use the turbo outdoors that’s probably a better option.
Edit: as for trainers, I got one of the higher end Minoura ones to replace an old tacx. Mainly because it had a wide range of resistance so was good for me and the missus. Seems pretty good. If it was just for me I don’t think I’d have bothered with variable resistance and probably would have got one of the kurt kinetic ones.
Double edit: Also found a close ratio cassette to be useful for turbo work so you can dial in just the right combination of power and cadence.