Qilue: Pretty bad advice.
Corvette
Corvettes are unable to reach meaningful amount of armor.
And actually it's better to build another corvette instead of adding armor to it.
Shields could be considered as extra health as corvette won't have much time to regenerate them. and lack of armor make them as valuable as health.
engines, special modules and other similar stuff actually decrease corvette efficiency per minerals spent.
As general rule try to keep them very cheap but with maximum amount of combat value. They will die in masses no matter what you do.
Try to design corvette with no shields, no armor, reactor I, sub-FTL engine I(FTL drive 2 is worth it's price), scanner I, no boosters and up to date weapons and compare it's real firepower and total health per spent minerals to current design.
also note that excessive energy increase firepower and evasion(only survivability of corvettes)
Destroyer
Destroyers have actually only one meaningful role: destroying starports before you get cruisers (cruiser is superior to destroyer in any possible role including fighting corvettes)
Unfortunately missiles are still very weak and get weaker as fleet size increase(there is a lot of threads on forum that cover that),
is you have available kinetic weapons then use them on Large/Medium slot. if you don't then use lasers with armor piercing.
As a general advice next time try to reach Cruisers faster as cruisers are capable of stacking either armor(to 75%) or shields and they are worth to spent minerals on combat computer/scanner/everything else.