I would LOVE to check those out! That sounds really interesting.
By the way, I also did a little work on something you might want to use for your infantry-based mod: https://i.imgur.com/N7tWkE5.mp4 https://i.imgur.com/yMbzj6C.mp4 This still needs color correction, but the basic frames and alignment are done. Each Engineer has a pistol now. Here's the sound effect: engi boi.wav Not particularly useful compared to standard infantry, but not totally useless either. An Engineer can 1v1 a Trooper, two can possibly take down a Shotgunner or Grenadier... this mechanism mostly just enables them to defend themselves against injured infantry, such as those that pop out of structures, and contribute to the infantry force while being escorted.
When you compare the Shotgunner and Engineer in my own mod, the former under normalized conditions costs 50 credits, is immediately available, takes 5 seconds to train, has superior armor, HP, and movement speed, deals 16.67% greater area damage, does 125 DPS, and stacks up burst a whopping ~45% better. The latter deals ~92 DPS, takes 30 seconds to train, costs 400 credits, and requires the Barracks upgrade and an Outpost.
There is no contest; Engineers can't be massed and used like normal infantry while you go storming the enemy base and capturing everything. They still rely quite heavily on the protection of other units. However, they're slightly more capable units and the pistol is a bit of flavor if nothing else.
That's for my mod though. If you have another idea of how to balance them, you're free to use the sprites however you'd like just as soon as they're finished, if you'd like to use them.