Do crewmembers ever "level up"? And how to make friends?

Crew would maintain a varied skill distribution if there is a maximum level such that nobody can max out every skill.
Gaining skill in fields through practice runs into the problem that a skill 0 miner is incapable of Mining.  They will never be able to try out mining.  On the other hand, Weapons 0 people can still fire guns.

My wish is to buy slaves from slavers.  They would cost credits proportional to how many skills they have.  A cheap slave could become more capable over time by gaining levels, or buy the skills of an expensive slave right away.  They could have a rebellion or higher surrender chance, so you have to keep control of them.  And obviously, the option to release the slave or, after earning sufficient experience, recruit as a full crew member.

That makes a lot of sense. Having a maximum number of possible points per char does work well. The whole attributes are fixed, stats can be affected by injury/mods and skills are flexible due to training/use/lack of use thing is tried and tested. If it aint broke....
I like the slavers actually providing some game richness in that way too.