Questions and need suggestions on performance

Hey there! I am new into SDL/OpenGL development (here too, nice to meet ya!) and I stumbled on a weird situation. I have a raw ARBG32bit image. I am still working on creating engine/wrappers for my learning project though, so I can’t test it if loading raw image (by loading it all in memory, to surface, to texture) is as efficient as loading an equivalent BMP file with dedicated function. I did had a look at source code but it was bit complicated to follow so I am not sure of it. Is it really okay to let it be this way?

Also, I wanted some suggestions on resources, and nope, not on basics, but rather some of popular/tested designs/tricks, since I am quite unexperienced in working at low level around things like this. I am trying to create a SNES-styled 2D game, and looking to try out lot of things inside it, as it is more of a learning project for me. I was thinking about multiplayer design and a thought struck me yesterday, if there is something like a boss, spawning mobs, and many objects, all with their own movement pattern relative to the universal frame rate, it seem daunting to iterate over every object in map and get their state, and update the objects texture, then place background, objects, player and overlay textures one by one and render it 60 times/second. I got an idea later to maintain queue of things in motion and update only them to reduce usage. Though, I am not sure if it would work out, and I am still using multiple textures (And yeah my engine is not ready to test it all, so who knows, PC might be able to handle that?)

I would love to know how those huge MMOs accomplish it, for example, I would appreciate any suggestions on resources to catch up with latest stuffs in game engine dev field.

And Thanks for stopping by and giving it a read!