Creating New REZ texture skins

I am getting ready to start making REZ texture skins, for maps and weapons. I have everything I need, including prior experience modding,. I have not, though, made an original REZ file, I have a question or two, about making a ,img etc. into the correct DTX file ,size ,etc, to conform to CA models.

Basically, how can I turn a picture into the skin on the game?
Does size matter when changing the image? (a 86kb 256 DTX original file, can u use a 171kb 256 img, or a 171 512 img,? or does it have to be a exact match, IE 86kb 256 image?
does it get bigger , the image, when u convert to dtx?

If someone with knowledge, true knowledge, would take some time and help me with this, I can guarantee it will benefit our community. Thanks for your time and help.

Read the tutorials
Editing .rez files
Every .rez file and what they control

Also, to answer your question, yes the edited image has to have the same dimensions of the original one.