Since you are a Souls vet, here is some useful info:
The weapons Parry score is the same as Stability in Souls. There are small differences between various individual weapons within any certain weapon class, somewhere in the 1-5 point range before you factor in the specials, which can grant up to +14 Parry, but the difference between the weapon classes can be pretty huge. Dual swords have easily the best Parry values, Axes have the worst. This can have great effect on how much you can/should be blocking with any given weapon type.
Other stat that affects Ki-loss upon blocking is Toughness, one of the things you get from armor, which also shares some elements with Poise in Souls. The more toughness you have, the less Ki you lose when blocking. Also, at exactly 200 Toughness, you will become immune or resistant to hit-stun from certain attacks.
And to touch on the equipment weight, yeah, you will never want to be above 70%. Agility A is under 30% and will give you the best Ki regen and the best dodges. Agility B is 30 < X < 70, with slightly inferior Ki regen and dodging, but still very viable. Agility C is shit.
As for the side missions, I preferred to do all of them as they appeared, but it can lead to a sense of fatigue to do missions in the same areas over and over again. And concerning levels, please don't take the level recommendations literally. Their only real function is to give some indication of the relative strength of enemies in any given mission compared to others and indicate the level of loot you'll be getting. Your character level has little or nothing to do with it.