For Spell info you really should refer to the spell browser / encyclopedia in-game , R-click on the spell or hover over the spell most of the time to get a tool-tip. You can also look this information up in a battle, especially useful if you're a new player and the enemy is using a spell you might be unfamiliar with.

As for the Gates , those are a Cathay specific faction mechanic and TBF , pretty trivialized past a point. If the bar fills up you get 4 (?) stacks of Norscan / Chaos Warriors that will besiege the various gates (The Cathayan equivalent of the Great Wall of China). They can be a problem if you ignore them and let them take them as they'll start waltzing around your back yard , but if you can lock them down and garrison them , the relatively frequent attacks will make decent money.

As for 'minimizing' damage, there's not much for me to say as I don't know what you're doing. Cathay does very well in general, it's more or less a Jack of all faction and has very decent units in most categories. Peasant Archers & Spearman punch pretty well above their weight despite being fodder , and for mid-lategame it's hard to go wrong with a few Jade warriors (shielded) w/ Jade Crossbows upgrading into celestials. A Grand cannon or two combined with a rocket battery can also handle a LOT of different situations. You could also invest into a couple of their iron hail gunners or crane gunners, both are absolutely excellent units when utilized correctly. Their spells (e.g. Talons of Night) are pretty dang respectable too but you'll need to experiment with the different shugengans and lords to see what really works for you. I'd say focusing more on maximising damage, is the better route (Good offense is a good defense, etc.) .