It is straight-forward, your marines are twice as strong with Advanced Tactics 5 (you lose half as many marines, meaning you only need half as normal), and crew gain twice as much XP with Command Experience 10 (and Making Do halves the crew need to pilot ships as well).
When crew gain normal experience, you will level enough Elites to crew your ships and some extra to replace losses and maybe sell a few. In my last 0.7a game, I had a few thousand elites beyond fleet requirements by the time I reached level 50, meaning I could sell two or three liners worth of elites once per game. If you max Command Experience, you can level twice as many at the same time, and you have half crew requirements. You can sell several liners worth of elites then.
When you fight, you level up only so much crew at once. Once your fleet and crew are big enough, you will not level everyone at once. If you have a big endgame-sized fleet, you probably have enough crew to level without the need of liners, much like there is no need for tankers unless you want to haul thousands of fuel for trade. Starliner is a relatively slow pig that eats more supplies than most ships. Using Starliner for anything aside from carrying personnel to sell is wasteful of supplies.
I have not tried human trafficking strategies because I want to focus on Combat and Technology skills now. Fighting with overtuned ships is more fun for me than grinding up assets.