2. i suggest & recommend you to change you pads to ninja 250's brake pads..they have better material quality and blablabla, but more expensive..the stock RTR's pads are bad, it'll soon wear your disc (right now i'm using yamaha's single piston caliper, since one of the stock piston often stuck)....the sooner u change it with ninja's pads, the better..
3. ehmm...can't say much for this..i've set my idle RPM for 1k rpms, and went to 1.1-1.2k rpms when hot....maybe it's because our country have a different temp and humidity
what's the NGK iridium plug's code u've bought? CR7EIX? CR8EIX? CR9EIX? or maybe SIMR8A9 (CBR 250R laser iridium plug)?