I watched DonamerDragon's run. It seems to me that the most sensible thing to do would be to run a test run from beginning to end and perform something similar to what he was doing.
1: Grab all spirits near path
2: At each boss, hack your elements to some combination of water/fire/earth/wind and test out various strategies with the amount of spirits you have.
We can look into how to hack elements because you probably don't know how. It isn't difficult at all compared to the time testing you save.
Anyway, essentially you want to see how to beat the 8 bosses optimally before executing the run. Also strategies for quick random battles are quite important.
I found a boss battle compilation, it includes a very cheap way of beating Fargo and Beigis.
http://www.youtube.com/view_play_list?p=3C478E73136A0372
Drain Magic and Confusion both seem quite useful for replenishing MP.
An interesting note: I believe Wind Cutter 3 will raise your MP twice as fast as Fire 3 because it is supposedly based off the number of hits. I always used Wind spells when I played this game, I think perhaps the usefulness has been underestimated in this thread.
According to a post on GameFAQs: - "Spirit Crystals will be gained while grinding MP, but I need to mention that only 98 can be gained through grinding, while the other 98 are floating on the world map for you to find."
4 starting + 98 overworld + 98 leveling = 200.