Spring RTS Engine

I've been searching for a game engine that might be able to accommodate something.

I've designed a game system that relies on players being able to customize equipment for their units before the game begins, and be able to access those loadouts during gameplay. In a nutshell, players design 3 types of Basic Infantry, 4 types of Advanced Infantry, 3 Officer Infantry (unique, can only have 1 of each active at a time) 2 Light Vehicles, 2 Heavy Vehicles, and one Command Vehicle (unique, can only have 1 active at a time), as well as picking five Specializations (each one basically unlocks different research/upgrades accessible in-game). The biggest balancing factor involved here is that the more equipment you add on to your units, the more expensive they are to build in-game.

I was wondering if this engine is capable of this, or if I should look for something else?

Sure it is, see for example zero-k's classic or DOTA customizable commanders.

There's also the perk system in THIS Happens In Space.

You might also want to look at the proof-of-concept-mod YAAG (Yet Another Annihilation Game), made by DeadNightWarrior. It has factories in which you can custom-make your units by selecting chassis, weapon, health, stealth, etc etc, and ofc better stuff costs more.