If you want to achieve this with Troop Events I suggest Yanfly's Base Troop Event Script (http://yanfly.moe/2015/10/18/yep-15-base-troop-events/). Everything you event in the very first troop (0001) is applied to every other troop in your game, this saves you a lot of copypasting.
AFAIK Battler Sprites can be as big/small as you like, so there's no definite resolution for a template.
As long as you make your image match this pattern there should be no problem. If you want to display static images for each state you could simply paste the same image 3 times side by side.
As you mentioned, this is often used as a more primary way of distributing stats, mostly seen in dungeon crawler games. And it works pretty well. I like stuff like that the most when it's kinda randomly assigned to characters and you have some way of always recruting new ones and perma death...
My brain when designing quests:
There is piano, it needs help --> The organ (yes organ now) is missing a component! --> Where the heck am I supposed to put this missing piece!??! --> Add an entire new mini dungeon specifically created to house this new piece. --> Connect this brand new mini dungeon to an already designed dungeon with background information about the town it's found it.
Sheesh, Guys, don't think you can throw easy prices like $25/$50 on potions/ethers then have monsters pay you $75 for killing them (never understood that concept btw lol) and think it'll all work out!!! Just realized my prcies vs payout left my players unable to get decent stuff without some serious farming from the start, i'm about to call H&R Block to help my MC get his stimulus check just to buy new armor