An update on a few things:
I think we can pretty much rule out a TAS of this game until we find out more about the game internals, specifically the RNG for random encounters. I did a short test a month or so ago, which I have now
uploaded. It's 10 minutes long. Consider it an example of how hard a full TAS would be. (Note the route has changed a bit since, see above posts)
I've done some low-level investigation into the assembly, but I am nowhere near good enough to find a RNG. I have browsed some material on the web for finding things in the ram and assembly, but nothing this complex. Since it seems to base encounters on number of steps, we need to know when the amount of steps before a battle gets set and manipulate it. Then we can proceed only when that number is very high (maybe using a bot if necessary). The same goes for being able to know that a battle will yield critical hits or appropriate behavior from enemies.
So...things to figure out:
random number of steps to a battle (both outside and in caves)
random numbers for battle effects (criticals, dodges, spells working, item drops, etc.)
random number for enemy formations (for getting metal slimes, etc.)