If you are going to use a large or heavy shield (kite shields, plate covered, heavy round, etc.) then 4-5 shield skill is fine. Going for higher shield skill isn't necessary unless you are using a really slow one (heavy board), or a lightweight/small shield (buckler, brown lion heater, knightly heater). Slow shields will block faster, and the "force field" and increased durability help the weak points on a lighter shield.
I have done 18/24 buckler shield build in the past. High agility and a light weight shield let you do fancy footwork that a slower, heavier equipped shielder cannot. Swords with a balance between stab and swing damage work best, but very fast short swords and daggers work very well too. With heirloomed mail armor, a light shield, and good awareness you can skip the Ironflesh points. If you plan to use shields that have a high weight, I would go for the ironflesh over maxed athletics/shield skill. When you are slowed by your gear, the higher athletics skill won't make as much difference (in my experience).
If you plan to use axes or blunt weapons 21/21 or even 24/18 may work better. They are slower, and you will take hits when someone beats you to the swing. I have not played much with a pick type weapon, but the general consensus is that an agility based build will work better for you.