Hi guppykid,
To start a new project/line/creation of a new strain is not a simple task but an enjoyable one if you obtained the desirable result or getting closer to the end result. You can find some of my old thread documenting some of my projects I've undertaken.
The advise I can give you is set your objectives. Have a picture in mind of what you really wanted because at times you might get a single male that looks spectacular but not the end result you aimed for and you get distracted and strayed from your actual objectives. Then you'll have alot of crossing/hybrid creation.
Secondly please do some research on guppy genetics. Some traits are dominant and some are recessive. Creating new line of guppy is not like water color i.e mixing white and black you would expect grey. If you are good a theoretical gnenetics, chances are you might reach your goal in the 4th generation. Some well known breeders spent 10-20 years to perfect a line especially if you are thinking of a solid colored guppy. Just for information, now these breeders are trying to breed solid white not platinum white tail but real solid non-iridescense white. And they probably will succeed within this few years looking at some of the specimens.
So hope this helps

and good luck with your endeavour.....