If it was as easy as that, we'd all be doing it.

If you can afford to purchase seeds, I don't at all see a problem with playing around. It's one hell of a learning experience, and makes a boring hobby more interesting. Keep yourself a 'progression' log, label all seeds and plants and selectively breed them how you'd like. Have a goal in mind, or it becomes a scattered experience with inconsistent progression. Might get lucky or good, and come up with the "eternal buzz" folks have been searching for since Ponce DeLeon found the Fountain of Youth. (that'd be cool, good looking and stoned forever...)

When cross breeding, the trick is to keep track of the differing offspring, and selectively breed the positive traits you are looking for in the cross. Tiz a little harder than it sounds, and often the crosses don't add up to a worthwhile (better than the parents) combo. That's why some patients pay the big bucks instead of breeding local bagseed.

My goals when breeding fresh seeds of incredibly expensive stock, (online seeds in general) is to breed as if purebred, and selectively breed to keep the strain within breed standards. (if necessary...most quality genetics have, at the most, two different expressions) My first seed run is always to breed organic untainted seeds and have them in-hand before I mess-around with crosses and femming. (always have a back-up plan)