Yes, you can! If 4 lamps bring you the light you want and need in your living room, you can use 4 lamps. For example, 2 table lamps flanking couches or chairs, plus 2 floor lamps on either side of the room...but really, the sky's the limit. You definitely can use 4 lamps.

We have four lamps in our living room, plus sconces flanking the fireplace. Three standing lamps plus one table lamp. I rarely use the sconces as I prefer the softer, warmer light shed by the lamps.

How do you match them? Can I use one with silver metal the other one with gold metal?

you can use any lamp you want so long as it has a matching element… the easiest way is with matching coloured lamp shades.