It should be pretty obvious that you need to talk to the local FSDO about a 141 approval. You'll be sick of it by the time you're done- it is a highly regulated system and every single word in your Policy Manual, which will be 30+ pages has to be approved. This includes further approvals to change anything. Here are some typical areas that need to be covered in a Manual.
Section 1 General Information
Policies and Procedures
Contact List
Safety Guide
Your Instructor
Lesson Preparation
Physical Condition
Student Progress
Course Completion
Dispatching Procedures
Section 2 Ramp Operations
Preflight Check
Ground Operations
Fire Precautions
Section 3 Flight Operations
General Flight Operations
Currency & Auth.
Traffic Rules
Local Flying
Cross-Country Flying
Flight Plans
Collision Avoidance
Fuel Reserves for Local Flights
Weather Minimums
Student Pilots
Section 4 Emergency Operations
In-Flight Emergencies
Dispatch Procedures after Precautionary/
Emergency Landings
Emergency Security of the Aircraft
Aircraft Malfunction or Damage
Incident or Accident
Simulated Engine Failures
Section 5 Winter Operations
Preflight Inspection
Fuel Contamination
Aircraft Fuel Filters and Sumps
Engine Starts
Taxiing
Takeoff
En Route
Letdown
Landing
Post Flight