As to the Instruction mechanic, I have some very specific thoughts, but in general the idea would be that rarity, access, time available and cost would be tied to how difficult it is to have an instructor that has both Instruction and the desired skill.
As a rule of thumb, roll 2d6 at or under pop stat of planet you are on to see if classes are available for a specific skill. LL and TL may be limiters as well depending on the skill in question.
Instruction-1 and Skill-1 yields taught Skill-0, and should be as common as adult education, technical school and/or junior college to get. 1d6 weeks to wait for the next class.
Instruction-2/Skill-2 yields Skill-1, and should start costing serious money to get- and remember, good chance it will take two tries to get it. 1d6 months for the next one.
Instruction-3/Skill-3 yields Skill-2, and would be the equivalent of getting a master at their craft, the class that is only provided once a year that everyone vies to get into, and makes careers. 2d6 months for the next class.
Instructon-4/Skill-4 yielding Skill-3 gets into rare territory, very few people even of a huge civilization are going to have this combination. Think 1d6 years for the next class, a lot of money, AND impressing the teacher with your potential.
Instruction-5+/Skill-5+ is a legendary teacher, a sensei, and there is no regular schedule for such capable instructors. This will only happen with the student being voluntarily taken on and showing talent, need, and potentially a lot of money- or none at all.
Each level of skill should require having the previous skill level, no going Skill-0 to Skill-2.
To be really harsh and limit the abuse of this mechanic, rule that if a character fails instruction twice, they cannot learn anymore from Instruction for that skill.
Cost IMO would be cost of instructor's time if they were doing the job x2 for facility expenses, profits, increased pay for being an instructor, etc., x level of skill to be imparted (treat 0 as 1). Divide in half for the six month part-time 'evening class' cycle rather then the intense six-week training.
For instance, pilots cost Cr5000 per month, intense training is six weeks so Cr7500x2= Cr15000- Cr 7500 for a relaxed class.
Don't forget to charge for living expenses during the intense version if there isn't an employer providing room and food.