What factors affect trade route profits

The manual says population of starting planet, populatino of ending planet, distance and starbase improvements. Is this all? Just wanted to know if the income of the starting or ending planet had any effect. And if you guys had noticed how distance and population balance out (which being more important.)

Final 2 questions:

I think this worked in a previous game but I have not confirmed: If you build a trade ship on earth, send it to Wardell V (your planet), put it into orbit, launch it, and then send it to dark yor do you get a trade route from earth to Dark Yor or from Wardell V to Dark Yor?

If you build a constructor and then upgrade it to a colony ship (because the starbase got built by someone else) will it colonize a planet with 1pop, 500pop, error message, or crash the game?

Thanks in advance!