Making a puppy, about 6" long, 4" high (ish) dont know best way to go about molding. Suggestions?

I'm no expert but I think it would be easier to do all in fondant than to try and use such little quantities of RK and get them where you want them to be.

To me, it doesn't seem like 6" long and 4" high is really that small. I think it would take a pretty good size piece of of fondant or gumpaste to get that size. I think if I was going to do it, I would make the body in RKT and the head/legs...everything else in fondant or gumpaste.

I agree. Use RKT for the body because it will take a pretty large size piece of gumpaste or fondant. I just made dump trucks and bulldozers out of RKT and they were about that size. I covered them in modeling chocolate which I made with the candy melts in different colors. Since it was so easy and they came out great, I can imagine I will always choose RKT over all gumpaste for any figure that is larger than a few inches long/tall!