Do I need to worry about deleting faces off my Walls etc.?

I have been building my Apartment as a sort of testing ground to put all the things I learn in UE4 into practice before actually making any game of sorts. And I already know to use Static Meshes and not BSP Brushes. I currently make the brushes and then convert them into Static Meshes because I’m not making complex geometry, just walls, simple shapes. I do have Blender for when the day comes, I just don’t want to overwhelm myself by trying to learn two different things like that at once and burn out.

But I have some free levels people have made and noticed that their walls and almost anything that was a structure had no faces on the other side of them. Is this necessary for performance, or can my Wall pieces have six sides to them still, or should I remove faces from them for areas a player might not see anyways? And is there a way in engine to do this to a static mesh? Or can I export my static meshes to Blender and remove the faces I want? I just want to get things right, and I have come really far in learning and this one didn’t even dawn on me that I seen plenty of maps that have missing sides when going into noclip mode to fly around.

I am aware of the split geometry tool, but I don’t see anyway to use it on meshes, only brushes it seems. I do build my Walls in module pieces, not giant chunks, just to be clear if that’s needed information. I also tried to remove faces from brushes and then convert them into meshes, but it only seems to work if it’s just a wall. I tried to do it with a subtractive box in it, and it reacted weird, and became solid inside somehow.

Any tips and advice would be wonderful, thank you!