I've been trying to decide if the right idea is to set myself up to run from every fight or if I want to set myself up to smash every fight. Both are doable within the confines of the system I think, but they do require different gear setups and things to power level.
Fighting every fight has the advantage of getting lots of money/loot drops. In a normal game it would also give more experience, but that's not the case here. It does give more chances to gain agility.
Running from every fight has the advantage of not needing nearly as much mana to beat a dungeon. It lets you build just for boss fights instead of needing to be able to kill a variety of trash mobs. (Ribbons may not actually be needed if you never actually fight anything that casts a brutal spell on you.) Running from fights is typically also faster than fighting them, at least in a game with a high success rate on running.
I loaded up my save file from my marathon playthrough and did some brief testing on running away. I tested by running with some with 99% evade, someone with 0% evade, and then I lowered the 99% guy down (to something like 15%) and tried again. Every time I tried to run at 99% evade it worked. Every other time it failed. This makes me think it isn't agility that matters for running away. It's just evade percentage. And if I want to I can get that up to 99% pretty trivially by dual wielding shields and power leveling the shield skill.
The real question is going to be if many fights are set up with a "can't run" flag. The database I've been using to pull data for the game doesn't list that anywhere that I can find, so it's going to be a trial and error kind of thing. I think I read somewhere that you can't run from undead, which could be problematic.
In terms of the fight plan I'd probably need to find a way to reliably kill all the monsters in one action. Autoattacking them all to death with berserk buffs will certainly work, but it isn't especially fast. There are instant death spells in the game, in particular the toad spell. Toad has the best accuracy of all the instant death spells and it's also needed for getting ribbons super early in the game. Convenient! Some enemies are going to be resistant to toad though, so I guess those fights are the autoattack fights. Or maybe I want to level up an attack spell like fire? Undead are also immune to toad I think, but those you can kill off with a life spell if you have enough accuracy.
I think the flight plan is superior to the fight plan, if it will work on most fights. I guess the way to find out is do a run with a 99% evasion character from the start and see! And probably level up a life spell to deal with undead fights if it turns out you can't run from those.