I've been doing a playthrough of the 3DS version of DQ8. Evading encounters really helps with modulating difficulty by level restriction. I've been having lots of fun with this.
I went for Spears, Axes, Staves, and Bows with any excess points put into their character skill trees. Levels listed in order of Hero, Yangus, Jessica, and Angelo.

>Geyzer, 5, 5
>Khalamari, 9, 9
>Tortured Soul, 10, 11, 10
>Trap Box, 12, 12, 13, 12
>Don Mole, 14, 14, 15, 13
>Great Argon Lizard, 16, 16, 16, 15
All of the bosses so far have been easy, not because they can't kill you, they can, but because I got lucky and took advantage of the alchemy pot.
Here I tried at 18, 18, 17, 16 but it didn't work out so I grinded a few levels on Gold Golems and made like 50k gold. The clincher for Dhoulmagus isn't multiheal, fullheal, or even insulate, it's Oomph. Without Oomph you just don't have the damage
>Dhoulmagus mage, 20, 20, 19, 19
>Dhoulmagus demon, 21, 21, 20, 19
Dhoul1 is much more challenging in a low level run and it's not even close. Having to deal with three enemies who deal 40-70 damage per hit up to 4 hits a round is just too much damage.
>Evil Jessica, 23, 23, 21
>Red and Blue Ogre Beasts, 23, 24, 21, 21
You might think how did Hero and Angelo not gain levels? They ate dirt and it was Yangus against the world and I got her beat down right as I used my last Lesser Panacea.
>Captain Crow, 24, 25, 22, 21
Captain Crow is a pushover if you just get Angelo sarcastic snigger skill, with it you can extend his psyche up + thin air spam by two or three turns between each and with the monster team you can just send them into to tank the hit.

Here's where I'm so far; 24, 25, 23, 22. I got Red and she always joins at level 33, good thing too because Empyrea is a pure level/gear check, unlike other bosses there's no way around it, she's just too sturdy. Gold Rush at 500/hit is the only way.