I said 5 shield as there's some strong 5 shield requirements out there (huscarl) but I personally prefer only going with 4 and using the knightly heater or elite cav shields.
I'd still recommend going 2 or 3 WM, once you get to around 120 WPF in 1h then I'd start going IF
And 15% damage increase for every 100 WPF (7.5% per 50WPF is actually very good, that's one more Power Strike basically) but I do not believe that is accurate, as I was under the impression WPF x PowerStrike (minus other variables like enemy armor/health and soak) are what takes your damage into consideration.
I personally think WPF is important (for both speed and damage as well as reduced upkeep chance), and these are offensive stats rather than hit points, which is defensive. A good offense (killing the enemy) is sometimes the best defense.
I think it's important enough that it's better than IF, but I use polearm and 1h WPFs so I need max WM, if you're just using one skill, you can easily get by with 2 or 3 WM. At 3 WM and 4 shield, he could still have 4 IF....I think that's the best of all worlds.
I revised my OP build to what I think you should use.