hELLO Dumbofon from the past. Apparently, you knew nothing about gamedev and stuff back then in 2017, so you wouldn't get that cameras instead of rendering to screens can also render to textures. They call them "Render Texture"s (for some reason, VALVe decided to call them "Render Target"s in Source, but eh, whatever). Now, I don't know exactly how Source is made, but I suppose to increase the number of render textures you must somehow tamper with the source code, which obviously you can't do because source code is secretly stored from us, mortals. But I believe though even if there was a way it would consume all your 8GB ram.
P.S. Maybe there is a way, but I obviously don't know.
P.S.S. Your engrish sucks.
P.S.S.S. *sad noises* happened when I saw this discussion with no replies.