And the number of textures that could be on the screen at once depended on the resolution (and possibly also the colour depth) of those textures. The PS1 had a megabyte of "VRAM" that the textures would normally have to fit into. If each pixel took up 15 bits (1.875 bytes), you could still have about 550 thousand pixels in the textures. So if each texture has 128x128 pixels, you could have about 30 textures. If you use fewer bits per pixel, you can fit more pixels in the RAM, but then you have fewer colours to work with.
The Saturn had 1.5 megabytes of VRAM, and theN64 had 32KB (which you could change multiple times during a frame to put in different textures but that would be somewhat slow, so that's why N64 games used fewer and smaller textures.
For now, I haven't had to use textures, although I guess I might have to at some point. The amount of triangles you can draw also depends on how you draw them, so if you go without textures or vertex colours and just give each triangle one colour you can get 360000 triangles on screen at once, texturing or lighting halves it, and using both texturing and lighting halves it twice.