I recommend starting with the Award Maximizer:
https://www.travelcodex.com/award-maximizer/
That will help you see which points programs can help you reach your goal. Take the other advice you've received about using points for the long haul segments and pay cash for the positioning flights. That will stretch your points and still give you flexibility in your outbound and inbound airports for the long haul segment.
I'm curious if the AA and UA point totally are really so small, or those should be in thousands.