1.5: Do NOT use a magic main character, honestly it's a waste. Yuzu is a fantastic mage, Midori isn't bad either. If you play your cards right you'll get Amane/Mari late-game and they're also good mages...too many mages. You don't need to make him another. With my godly team, it's my melee MC and 3 magic users.
The problem with this is, until much later in the game, Magic-based skills outnumber Strength-based skills by AT LEAST 3 to 1. For most of the early game, you're forced to have Atsuro in your team, and you have to save both Keisuke and Midori (tough to do on a 1st cycle without a FAQ) to even have the option of switching him out. This leaves you with two physical fighters for most of the game, and you might find yourself without enough skills to equip both characters to their fullest potential. A Magic-based main character is best for a first cycle, because then you have access to more elemental spells on your team. I'd say you could make a reasonably good Phys MC on a second cycle run, because you can carry over skill cracks rather easily no matter how well you do (it's a measly 10 title points to carry over skills), and then you'll have access to more Phys skills from the get-go. Additionally, while physical attack and defense are separated into two stats (St and Vi), magic attack and defense are in one stat (Ma), which makes specializing easier.
2: Get magic focused demons with your melee focused main character. I always made the mistake of getting melee with him, but that makes him useless for about 3/4 of the game, until good melee demons are available.
Wrong. There are plenty of good demons for both sides throughout the game. Jaki and Snake demons are excellent for battlefield control and tanking; their racial skills restrict enemy movement. Most Beasts (aside from Kabuso) are Strength demons, and their Animal Leg skill allows you to bounce around the field like a madman. Couple them with a Wilder and you can perform hit-and-run attacks which leave you well out of reach of your enemies. The lowest-level Kishin is 16 (Ubelluris), and coupled with a Beast, it gives you essentially two turns per turn. Genma demons, available from level 7 (Jambavan) also increase turn speed by reducing movement costs. Hell, even most Avians are slightly Strength-based.
3: Always keep magic focused demons with Yuzu. Her damage output is godly after she levels up a bit. Make sure your demons and Yuzu share at least one element with their attacks (IE: both demons have miragi and yuzu has fire dance). If you can though, try and get two that are the same on all 3 of them for maximum versatility and damage output. Third skills should be healing or recarm for later game.
Yuzu, due to her limited mobility, is best used as a healer. Stick a Fairy, Femme, or Megami demon on her and have her spam Charm, Devotion, or Affection. If you give her a Wilder or Avian (or possibly a Vile or Dragon, but I recommend never using those except as fusion fodder), she could be used as an attacker, but most Wilders and Avians are Strength-based.
4: I still have no advice for Atsuro. I find him completely useless. I tend to stick a Wilder demon (devil speed) and dragon (2 reach) on him and have him weaken or kill stronger looking groups of demons from a safe distance. I tend to keep ailments on his attacks and focus him with melee. Switch to the 3 reach demons I forgot the name of when they become available.
EDIT: You should be able to get +stone pretty early, and it triggers a LOT when atsuro attacks. If you do that and attack the middle of a group, you can generally take it out easily from a distance.
You find Atsuro useless because you use a Strength MC. He's an excellent fighter, and coupled with the right demons (see above), he'll do a good job cleaning up enemies. +Stone is fun, though I typically put it on my secondary fighter (in my first cycle, it was Gin, because I let Keisuke get killed -_-; )
5: Keisuke, I tend to have him with fast demons. Generally a wilder and an avian (flight) so he can easily get to objectives before it's too late (such as when you have to save people from demons). As for skills I honestly just give him whatever I have left...I never have a solid build for him. My MC and Yuzu do 90% of the work in this game (until the last day anyway).
Keisuke is the one I truly found useless. He doesn't have a specialty, meaning he lags far behind the rest of the group in damage. This gives him very little in the way of actual combat ability. I have the same problem with Gin. The only benefit to these two is that they have enough Magic to equip Grimoire, so they typically end up being my status-effect team (Paral Eyes, Mute Eyes, Weak Kill, +Stone, Attack All, and Grimiore). Also, Avian and Wilder are pretty useless together. Yeah, the Avian gives teleport, but the Wilder Devil Speed ability overrides the Avian +1 movement. Wilder is better combined with Genma, which will reduce your movement costs and make your next turn come faster.
6: Switch out Atsuro for Midori if you can, and make her a tank healer of sorts (put healing skills, and skills to reduce the damage she takes on her).
I say dump Keisuke. Atsuro's more useful, especially for a guy using a magic MC like the TC.
Things to look for:
1: Deathbound. Get it as soon as you can for your melee MC. It does fantastic damage with high str and vit.
1.5: Drain attack. I forget if that's specifically what it's called, but GET IT. My main character's deathbound (after high HP cost for the attack) would typically completely heal him. It's insanely useful
2: In the second last fight of the game (I don't wanna be spoilery), one of the skills you can crack is multi-hit. This skill is the most insane skill in the entire game. If you play a newgame+ and get your MCs str and agility up, it will 1 shot ANY non-melee reflecting enemy group. Putting it on melee demons will do the same. Basically...get it at all costs. But do be careful because the enemy with it can also likely 1 shot your party with it.
EDIT: and if you do do that, get a 3 reach demon like Arioch, and a Kishin (attack twice per turn). Because it basically allows you to snipe 2 enemy groups per turn. Incredibly handy.
3: I'd suggest getting recarm, samarecarm ASAP. You don't want to miss your chance to, because you WILL want them (both) by end-game, because you will die... a lot.
Most of this I agree with, although I'd never use a Vile or Dragon demon in actual combat. The drawbacks of Chaos Wave and Evil Wave are too heavy (they both delay your next turn and deny you Extra Turns, and the Vile version - I forget which one it is - also reduces your movement by one) to be worth it, in my opinion.