Parry power is a multiplier of a shield's blocking power. Round shields give x1.5, bucklers give x2.5, and tower shields give no bonus (you cannot parry with a tower shield). Blocking skill multiplies the base Block Power of your shield (x0.4 at skill level 0, x1 at skill level 100). Since it increases base blocking power and Parry is a function of blocking power, then yes, Blocking skill increases overall Parry capacity.

As to question 3, I prefer round shields and bucklers, specifically for being able to parry. For how I play, the marginally higher blocking power on tower shields just can't come close to what you can get with a parry.

Finally, if you're already at the point of replacing older armor with iron armor, then you should also switch out your bronze buckler for an iron buckler. Both have x2.5 multipliers for parry, but the iron buckler has a much higher base blocking power (a level 1 iron is the same amount of defense as a level 4 bronze).