That is a very cool frame for a scratch built one and your first attempt!
As for the motors, the MT3510 motors are bit big if you only plan to use 12inch props on them, so if you want to use those motors I really suggest you consider using 15 inch props with them to get better efficiency, but I am not sure if these will fit onto your frame.
However if 12 inch props are the biggest you can fit on your frame then its probably better to use our 880Kv motors
As for the autopilot the mini unmanned hawk kit is a great choice since it is small, and includes all the extra adorns like telemetry, GPS etc… It is fully compatible with pixhawk in terms of software and missing planning. However since your frame is made using carbon fiber you will need to mount your GPS on top of the frame as carbon fiber blocks GPS signals. Also take some care when mounting the telemetry modules and your radio receiver since the carbon fiber does a good job at blocking radio signals. So just make sure the antennas stick out.
As for the radio TX/RX I would highly suggest you consider the FRsky Taranis as it will last a long time in this hobby, but if you want something cheaper the Devo 7 is also a great option.
If you have any other questions or need some advice please let me know and will also be great to see how your quadcopter build progresses!