1 - EASA doesn't allow Mode-S elementary aircraft to couple the Mode-S and GPS to send position data on the ADS-B link, so detecting Mode-S aircraft with a cruise speed of less than 250 kts is going to be a challenge
Technically incorrect. EASA permit input of non-certified GPS to 1090-ES capable Transponders including those limited to sub 175kts/15000ft. If connected and information is transmitted in the extended squitter, they may not include the integrity information which allows the information to be used for traffic separation.
If you want more chapter and verse, I recommend contacting TRIG.