1. Yes, it could be temperature related.
2. Yes, it could be fluid related (due to temperature affecting viscosity, mostly, but dirty fluid could also make it thicker).
3. I doubt a steel braided line would help in this instance. It'll add less resistance to flex from pressure, which increases feel.
4. Your hand could be out of shape from the winter, or the cold can make it feel like it.
5. No.
6. a. The clutch rod could be bent and/or hanging up on the seal.
b. Crud buildup under the countershaft cover could also impede the mechanical bits (I'd probably look into this one first).