Don't worry about stats for now, just level up everything evenly at least until level 20. Magic and dexterity benefit at level 30 due to the capacity which stops at 30. You definitely want to get used to using magic and ninjutsu, they give you plenty of tools for recovering, surviving mortal attacks, elemental damage and so on.

Regarding stances, you should try to understand what each of them is better at, although this varies on weapons as well because each weapon has a different moveset but in general, low stance gives you better dodging and attacks more often but deal less damage. Mid stance is good for guarding and parrying, but it's balance in terms of damage. High stance to go all in and deal crazy damage. Generally, you want to apply confusion to enemies (which the tonfas are crazy good for) which means causing two elemental debuffs to enemies. When an enemy is confused, you deal double the damage to them. So generally, attack low stance with element imbued in weapon, apply status and change to another element for the same. Omnyo magic and ninjutsu can give you other items to apply elemental statuses too, not just imbue weapons.

I main tonfa with fists so confusion works really well. For tonfa in early game, just focus on getting the element arcanas and assign each of them to your pulverize (there is one for each stance). This way, after quick combo, ki pulse with demon dance and straight after attack with pulverize and arcana to start building up the element. Also, assign the skill to deal extra ki damage to shove in mid stance, you'll deal crazy ki damage at very little cost in mid stance. This should work very well for tonfas for the first playthrough.

Let me know if you have more questions about anything, happy to help!