Running SITL Missions with Mavproxy for specific models from chosen GPS location [SOLVED]

Edit: Seems a lot of my questions are answered here https://ardupilot.org/dev/docs/using-sitl-for-ardupilot-testing.html

This is a pretty general question so I am not expecting a step-by-step answer.

I have had no problem setting up SITL with Mavproxy and Mission Planner and flying around what I assume is a flying field in Canberra. I would like to run simulations at my own locations and have use my own parameter files for actual aircraft I fly. Can I accomplish this with creating a mavinit.scr script?

I have read through the documentation and looked an the sample mavinit.scr file but I am still a little unsure. In the example file I saw raw IMU data which was not referenced in the Wiki and as far as I can see these are not Mavproxy commands.

@alias add ggyro g degrees(RAW_IMU.xgyro0.001) degrees(RAW_IMU.ygyro0.001) degrees(RAW_IMU.zgyro*0.001)
@alias add ggyro_earth g earth_gyro(RAW_IMU,ATTITUDE).x earth_gyro(RAW_IMU,ATTITUDE).y earth_gyro(RAW_IMU,ATTITUDE).z
@alias add grp g degrees(ATTITUDE.roll) degrees(ATTITUDE.pitch)

Can I use a mavinit script to load models with my own parameter files at my own flying location? Have I missed some existing documentation other then the Mavproxy wiki pages? My ultimate goal is to be able to fly more realistic simulated missions for specific models. I assume I could start a Mavproxy sim session with my own paramter file using whatever branch of Ardupilot I want and then connect Mission Planner and upload Missions and use a Taranis Joystick.

Sorry to ask a very general question. I am comfortable working in cygwin64 in Windows 10 and compiling Ardupilot so that is not a barrier. If anyone has any pointers I would be very appreciative – I am happy to figure out things by myself if I know the path…