i think you do not want deep charge on an ASP, but the optimized mass special effect. deep charge is better on very small FSD (class 2/3/4)
on the main upgrade, you might want to get this last half blue point on the progress circle to make it "done" but you wont gain a lot except the satisfaction of having it to maxxed.
remember you can switch modules between ships
also, the engineer will sell the modules he can mod. you can take your asp later to deciat, store the FSD you have engineered, buy a smaller one, engineer it, store it, take back your asp FSD, fly back, and remotely move from deciat your other FSD
that s quite convenient for ships that wont make the travel to Deciat fast enough.
example : FSD for an eagle. you dont want to go to DECIAT with an eagle, believe me
)
also, for my elder son, i made a 'quick exit' FSD with fast charge so he can run away from a bad fight in 2 seconds instead of 10.
welcome to the world on engineering
and, well, if most of "us" have engineered many ships, it s also because we ve been playing for a long time.
recently i fully engineered a fer de lance, it took me almost all the mats i had and nearly a week. i feel you when you say "fatigued". but it s always worth it.
and finally, unlocking some engineers will be a long story. but if you get the RolePlay spirit, it s an adventure worth living