Since people is asking much about this gona summarize it all. If anything is wrong or incomplete, feel free to post below so I can update this...
1st Ninja classes.
-Genjustu = Spirit
-Taijutsu = Wrist
-Ninjutsu = Wrist
2nd Some concepts.
-Physical attack and defense are modifiers influencing attacks from taijutsu and ninjutsu users.
-Strategy attack and defense are modifiers influencing attacks from genjutsu users.
-Block refers to parry, you will get hit but with a reduced damage, often producing a counter-attack.
-Dodge is to evade being hit. The ninja being avoided won't get any rage.
3rd Gear attributes.
-Physical = upgrade your hitpoints.
-Wrist = upgrade your physical attack and defense.
-Spirit = upgrade your strategy attack and defense.
-Swift = upgrade your agility and speed.
-Crit = increase your critical rate.
-Hit = increase your hit rate.
-Parry = increase your parry rate.
-Dodge = increase your dodge rate.
4th Colours and qualities.
-White = low quality.
-Green = medium quality.
-Blue = high quality.
-Purple = epic quality.
-Sets and materials go on ranges lvl 30-50/50-70 and I guess it will continue same as we level (I'm stil 59 so I cannot know ).
-Sets give more "extra stats" when you get more pieces of it.
-2 pieces, +physical // 4 pieces, +spirit +wrist // 6 pieces, +injury rate.
-Injury rate is the chance of creating an extra turn (anyone correct me if I'm wong about this since I'm not sure).
-Lvl 30 common material isn't same as lvl 50 common material, and the amount increases from one set to the other.
-Lvl 50 sets open a new option, upgrade, purple set becomes gold and for it you need many more common materials than for normal.
6th Jades. Will edit.
Don't get ruined by seeking for the perfect attribute and remember what you got on your other ninjas. Imagine you got 2 genjutsu users, always refine the item with worse stats, you can always swap the equipment between characters in case output happens to be better.
Boosting one or other is up to you, I cannot say you will get a winning strategy by doing this or that since the other may have a better strategy to fight against you. Also it's important to have into consideration the character basic stats as the talent it got. So with this basics go ahead and try what you like the most and find your ninja path!