while I am working on my topology I am confussed about internal, opengl and cycles

1.)

I was wondering. I never learned internal because well, cycles came out when I got started. now I was wondering, with painting and using image textures. do colors help with diffuse ? or is this only used for color painting and not using any image textures?

  1. )

I read the camera should have the focal length, sensor, and the aperture setting set right to get a good image. but if I switched to say super cam 35 I could do large scene would this mess up my uv and images because I set them to say 2048 by 2048 but my render says like 4k and 16:9 ratio? ?

3.)

as for my last question, it does seem that internal can do good renders like, I sometimes like the basic renders and I once saw parallax mapping that was cool to. open gl and cycles though, seems to make the renders well compared to internal more real or nicer. is open gl the same set up as internal but you render it as a opengl in the render settings?

  1. can you paint and do textures in internal then put the file into cycles?

I would like to know though how to set up a openl gl. I cant find a tutorial on that.