I do not think that there is one (or even the best) way to learn sculpting,
but You will not learn how to sculpt if you buy this manikins (IMHO).
Start from wire armature, and do it yourself from the beginning. For the start it's better to do a bigger scales - it is less frustrating. Later when your skills improve you can move to smaller scales. Sculpt few figures that are not so detailed, concentrate on anatomy and proportions- and then toss them in the garbage
Do a few more, and you will be closer to Your goal. If you are ready to spend some money - I would recommend this:
http://americanfinearts.wordpress.com/2011/04/08/john-brown-sculpture-dvds-in-and-ready-to-order/
Brown works bigger scales, but I like his way of explaining things, and knowledge you get from this can be used in any scale...
Small parts of this DVD-s you can find on youtube.
Also search youtube for sculpting timelapse videos - you can learn from other people's work.
Practice, practice, do some more practice (even play-doh is good as a material for that purpose), and then, when you get some basic skills you can choose your scale and move to the materials that are best for that scale...
I am learning how to sculpt for 3 years now, and I think that I just "finished" with the basics, or as Churchill once said I'm on the "end of the beginning", so do not be discouraged if you do not suceed at first- it is time consuming process
BTW: Someone else could give you totally opposite directions (and they probably would also be valid), this is just my "point of view"