Glarb pretty much said it but...
If you get good enough range or magic you won't even need windmill. I get by just find with just r8 windmill and I hardly even use it. If you do rank windmill though and you never plan on becoming a melee elf like glarb (you'd prolly be better off as a giant or human with melee anyways) rank 9-5 windmill should be enough too.
However if you plan on abusing field bosses then get at least rank 9 windmill anyways. Windmill as invincible frames which can really save you against the field bosses and various other crap mabi throws at you that likes to beat you up with melee. Otherwise if you got good magic ( r9+ bolts and some adv magic) or decent range (when i say decent I mean atleast r1 ranged attack ) then you'd be set for everything else. As for crap with Passive defences always be ready to fire a magnum shot or firebolt.. or a windmill. Those things won't flinch from most other attacks and smash can be risky.
If you really want an easier time in Mabi go with a human. Then you get the other two races (giant/elf) for free anyways later on.
ggFTW Rules★ggFTW Events★comedy.mp4
My fingers trace lines of azures and scarlets, following the viridian milky ways above
To the poetry of fourteen billion years of light that mellows my heart into a melody