I'm fairly new to Shogun 2 but have been playing multiplayer quite a bit over the last few weeks.

Recently some of my veterans have begun reaching level 5 and I am hesitant to invest clan tokens in skills unless they are worth it. I am also concerned about skill investment on hero units and Sengoku Jidai units seeing as these cannot be replaced. And also are there good times not to spend points to keep units cheap?

My assumptions so far have been that charge and melee attack are good for cavalry, melee defence and morale is good for yari ashigaru, accuracy and reload speed for bows and melee attack / defence for katana.

I understand, of course, that what is useful will depend on how I use these units but I just want some rough guidelines on what is actually good before investing my clan tokens or risking my unique veteran units.