RAM is never a problem. VRAM might be one.
Having VRAM occupied is generally not a problem unless you're overdoing it. Problem is, with such lack of details, it's hard to say if you're overdoing or not. But I can say with confidence that at the size of VAM scenes ( so generally, tiny/mid size spaces ), unless you'd put thousands of props with zero optimization, it's highly unlikely you'd ever kill your VRAM.
On the subject of on/offing atoms, if your assets are loaded, they're in memory. You will not optimize the memory cost after the loading process by simply putting the atom in off state.
For lights, if you're lighting the scene properly, memory shouldn't be a problem. Unless you're trying to achieve an effect (like a fade), putting them to off state is better. If you're overdoing it (like for instance more than 3 lights overlapping), your GPU is gonna take a hit way before the VRAM is going to be a problem (especially with the amount of VRAM we have now).
Now for the memory itself: it's highly unlikely you will have frametime issues because of assets. Unless you're filling the VRAM completely even before the scene is started... which is going to be a problem if you are in 4K for instance (which requires far more VRAM). If you are in that situation, you are probably using assets that are not very well optimized... OR putting far too much shit in your scene
