Cabin Crew Members:
You only need one passenger to require a cabin crew member.
JAR-OPS 1 Subpart O 1.990(a) explains it all. (Or EU-OPS, same reference.)
The determining factor is maximum approved passenger seating configuration. If your aircraft has 19 passenger seats and one passenger, a cabin crew member is required. The MAUW is irrelevant.
Noise Abatement:
ICAO Doc 8168 Part 1 Section 7 Chapter 3 Appendix 1 describes in detail the two noise abatement techniques.
NADP 1 (Close in sensitive area): Min height 800' reduce power, leave flaps in T/O position, climb at V2 + 10~20kts. Accelerate and clean-up at 3000'.
NADP 2 (Distant sensitive area) Min height 800' accelerate to Vzf and reduce power with first stage of flap/slat retraction or after flap/slat retraction. Climb at Vzf + 10~20kts until reaching 3000'.
Hope that helps, if it doubt, look it up in the source material!