Tareq, that's a lot of questions. I'll have a stab at a few.
I haven't done any colour processing but from what I understand it's much more precise (with no room for error) than black and white processing, which allows you to experiment with dilutions, agitation, chemicals, etc. For colour it's almost always the same -- you can't really change the process of development (for the most part). In addition, if you get an enlarger you would need one that could do colour, as well as getting another set of chemicals for the paper. Black and white is a separate process (film, chemicals, paper) entirely -- from colour. The only exception would be chromogenic black and white films like XP2 that can be processed in colour chemicals.
As for process...it's really the film that makes a difference, not the process. There is a difference between slides (positive film) and negative film as well. If you want prints, go with negative film (like Ektar, Portra, etc). If you want to project slides, or maybe only scan them, then you could try positive film. You can cross-process slide film (E-6) in negative chemistry (C-41) but the look will be different depending on what type of film you use.
Film used to come in a great variety of sizes, but for the most part they now fall into 3 categories -- 35mm casettes, 120 (or 220) roll film, and sheet film. You're probably familiar with 35mm film, 120 film comes on a spool with a paper backing to block light -- it's used for medium format cameras and will produce different size pictures depending on the camera/back that you have 6x4.5, 6x6, 6x7, 6x9, 6x12, etc (that's centimeters). Sheet film is like a sheet of paper (but film), it comes in different sizes --4x5, 5x7, 8x10, and larger (that's inches). Each sheet is exposed and processed individually. Of course, the larger you go, the more expensive each frame becomes.
Hope that helps.