I figured I ought to post what I thought was a good low-to-mid level build. There are lots of options and I am sure this isn't the best, but it worked well for me.
Choose sword-or-spear and kusarigama. Sword does good damage, lots of early game elemental sword options, great grapple/final blow damage, usable skills for low tier. More ki = more hits / able to dodge. Spear = more hp, but personal preference. Kusarigama secondary weapon handles crowds well, high-stance strong cheese, and low/high quick attacks break Yokai horns reliably, foot-sweep skill lets you final blow revenants / human bosses.
Choose Daiba-Washi as guardian spirit. Luck = better loot, and +equipment drop = more loot. Better equipment makes significant differences, particularly early on. Heals after using it, easy to refill the gauge. Isonade is better for fighting early on if game is too difficult, then get Daiba-Washi later.
Increase spirit to get all guardian spirit bonuses, then work on body 15ish, heart 30ish, 20ish dex/magic, base stats for min requirements to wear Warrior of the West, then Kingos/Iga gear later.
— Novice: ki pulse abilities, grapple, sword ki
— Adept: kick, morning moon (this is great vs. tachibana / early human opponents / horned yokai)
— Later: Iai Strikes, haze
— Much later: pimp back striker skill
— Novice: ki pulse abilities, grapple, tangle strike
— Adept: foot sweep (revenant killer), reaper
— Later: final blow damage, +rear damage, tangle strike 2
— Much later: super scythe skill
— Blinding Shell, Sneak Attack, Power Pills, Makibishi
— Later: quick change scrolls, shuriken, kunai, shuriken skills,
— Much later: projectile omfg skill and complement with spear thrust damage skill (+shuriken/kunai damage)
— Pure Mind 1, Resistance Talisman if you have problems dodging vs. Hino-Enma or poison in the mines
— Devigorate 1 / Carnage+Steel / Weakness
— Guardian Spirit Talisman / Luckbringer
— Much later: power word instant-cast
— Luck, Toughness to 20s, CCD, ninjutsu, onmyo, item drop %, amrita earned, living weapon durability
— Get passive skills from other weapon trees
— Join the furuta +luck clan because loot is where it's at early on
We're in it for the long game. Daiba-Washi + guardian spirit talisman + final blow from sword to kill all revenants (and some human bosses). High luck + equipment drops early means mo' money, mo' materials, and mo' chance to get something better from bosses/sub-bosses. You become a buff/debuff machine early on, blind is fun, carnage+defense makes stuff hurt more/less, weakness, etc. I read suggestions rushing to NG+, but… just have fun. Play the game. Co-op. I know that SSS temple blind now. Try beating bosses solo. I still have no idea if Umi-bozu can be blinded since it has no eyes, but damnit I throw blind powder on him anyway. Kill tons of revs because you can, easily. I will say red demon set + spear is good for umi-bozu primarily since those turds are vuln fire but you can use bombs too since they give you 1000 of them. When you find that first close combat life recovery inheritable weapon, just keep SM to your main weapon as you progress. Realize damage from behind on weapons increases final blow damage if that's all you have available. Use the other weapons for skill points/titles but don't put points into stats for them. Understand how they work so enemy attacks are familiar.
Later… NG+ you farm all them revs right off. Kill any 2+ sword-whatever-that-icon-is revenant you see. Everything I needed was right there, or within a few missions. I had 1000+ cups from just doing garbage in NG, use them extra loot every mission. Use something like 4 Kingo + 1 Master Swordsman to get 200 toughness, Kingo Sword (+20% rear dmg), switch to Kodama bowl for non-boss fights. Get that sweet shiranui off of some rev (15% CCD one, you can SM +heart/dex/whatever). Look for Iga Kusarigama. Level up these three weapons. SM armor occasionally, but SM your weapons when you can. Play the game. SM +attack to your gear if you like, or +amrita, or +luck. Who cares. Just have fun. Keep levelling up your weapon stat (heart) and dex, kinda of 2:1 or 3:2, 20ish Spirit, 30 magic (max onmyo slot cutoff). Once your dex is like 40-60, get unlimited ninjutsu on chest/arms, wear 3 pieces of iga gear + iga kusarigama, get some shadowround talismans, use the Gyokuto spirit (+100 ninjutsu) or Daiba-Washi (+luck/equipment) + LW to replenish low ninjutsu items, or on rare occasions Kato for certain boss fight levels (+skill damage for reaper). Switch between the kingo/iga setups for what is needed: close/personal, ranged, or hybrid. The options really open up around this point to where tossin' groundfire traps to beat Maroboshi, reaper madness for Hyakki Yagyo, kunai barrages to take out annoying enemies, etc. NG+ Yamata-No-Orochi loves kunai, and lots of them. Return to Gordo was even possible with groundfires, kunai, spirit talisman, etc. No lie, that was hard at this point, but doable.
Oh and for the Giant Frog +weapon/armor grind: carnage+luckbringer self, then sloth+weakness+blindness, run behind him, stabby-stabby, repeat. +4-5 weapons now available. Repeat.
I found 3 yakisoba mimosas before completing Return of the Gordo. 2 from normal fiends, one from a Lickitung (http://bulbapedia.bulbagarden.net/wiki/Lickitung_(Pok%C3%A9mon)). High luck? It helped a little, but didn't make-or-break anything as my first one was around the end of region 3. Tried farming for one, but that was stupid. Spent 4 hours for nothing in the end and decided it was stupid and went back to just playing the game.
I'm sure I could've tried to make this more explicit, but the game is meant to have fun, so… this is just a general idea for things. So many things are 'broken' but I think it's meant to be that way. Blindness is hilarious. Sloth is ridiculous and maybe needed in some parts (Tenguturd on the small ledge walkway in Demon Returns level I'm looking at you). Groundfire traps vs. Nobunaga in Gordo Returns, or Maroboshi bosses are just stupid. Throwing 60-70 kunai vs. anyone that's blocking is ridiculous.
Once you're at this point, you can pretty much reset and do anything, grind for another 40 hours, be level 750, turn into an accountant, etc.