Re: Does size matter...
As Lorien pointed out, size (here, how big your arms are) matters awhole lot when applying hand-wrist-arm-grip techniques. This even matters when using the whole body leverage, just less so.
In general though, I'd say MASS matters more than size. (Of course mass is proportional to size, as is strength) There's only so much leverage to be found in every situation. Even if you get the maximum leverage possible there is still a limit where the mass/strength of the uke can prevent a technique. (Kuzushi notwithstanding)