Sounds like something C3 could handle no problem.
A 50 x 50 pixels image at 32 bit depth should be around 10 Kilobytes (just tried it by creating one in Windows), which isn't a lot. 500 images of 10 kilobytes would be 5000 kilobytes, which is 5 megabytes, which is still a very small amount of memory.
The total amount of memory taken shouldn't be a problem at all, as for the rendering...
If you create an animation with 500 different frames, C3 ends up packing everything together into as few textures as possible.
Just tried out doing that in the editor to see what would be generated, I created an animation with 500 frames, then right clicked on the project folder in the Project bar and selected Tool > View sprite sheets. C3 ends up creating 8 textures of 2048 x 2048 which will take up 32 megabytes in RAM, which isn't a lot.
Since all the instances will be of the same object type, it means they will all use the same textures for rendering, so no memory overhead there. All the instances will use the same 32 megabytes of loaded image memory.
Finally, 75 instances will not be a problem at all.