I understand your comments about size impacting weapons, but I normally cover that with roleplaying. Feel free to establish min size requirements for using various weapons (and when 2H weapons become 1H).
To determine if a a weapon is one-handed or two-handed I was use the following general rule:
One-handed weapon has a length of up to the hip of the character, while two-handed weapons have a length greater than the character's hip.
I have the following exceptions:
All missile weapons require two hands to operated, no matter the size.
Pole weapons that can be thrown can also be used one-handed but at one attack size lower than normal. (i.e. Spear is a Large Puncture when two-handed and Medium Puncture when one-handed).
Also Short Blades are equal or less than the length of the characters.
This also affects which skill is used for a bladed weapon. A human would use a broadsword within the Long Blades skill group, while a Halfling would use the Great Blades skill group. A human would use the Short Blades skill group for a dagger, but for a Halfling that would be the Long Blades since the dagger is much closer to a sword for him. So Halflings do not have Short Blades weapons unless the get undersized daggers (Tiny Slash)
I would like to use size to simply this. Perhaps the character's size could be treated as an attribute rather than a racial trait and still have the Large/Small Size talents.