I've always felt that Helmets and Armor were the hardest choices to make. After a lot of research I've found some matches that I think are very good, but I haven't been able to decide which one to commit to.
Divine Veil + Skolver Coat
Has defense against all four damage types and resists fire, shock, curse, and freeze. Has a damage bonus of medium for swords and a medium damage bonus vs. Fiends.
Chaos Cowl + Justifier Jacket
The normal and piercing defense compliments the normal and elemental defense of the Chaos Cowl. Has a medium damage bonus and medium charge time reduction bonus with a medium attack speed bonus for guns. Has an adequate resistance to stun attacks with a mild weakness to poison, fire, freeze, shock, and curse.
Chaos Cowl + Shadowsun Slicker
The normal and shadow defense compliments the normal and elemental defense of the Chaos Cowl. Has a medium damage bonus and medium charge time reduction bonus making for a very high damage bonus for guns. Has a slight resistance to poison but a weakness to fire, freeze, shock, and curse.
Chaos Cowl + Chaos Cloak
Good normal and elemental defense with a very high damage bonus and a very high charge time reduction at the cost of a weakness to poison, fire, freeze, shock, and curse.
I mainly play as a hybrid sword and gunner. I plan to get the Crest of Almire as my primary shield. If someone with more end-game knowledge could lend some light on this I would be grateful.
Yes, your combinations are entirely reasonable. Yes, you can mix and match sworder and gunner armor. I would downgrade Justifier, for the reasons outlined below. Consider also Perfect Mask of Seerus, if you plan to get Operation Crimson Hammer access. Also, since you play mainly as a hybrid sworder-gunner, you might find my detailed sword guide useful.
In my opinion, your post focuses too much on damage protections. Let's recognize that armor does four things for you: resists statuses, protects against damage, gives you health, and gives you offensive boosts (abilities). Almost all 5-star armors give you exactly the same amount of health, so there's little point in discussing that. The other defensive benefits should be prioritized like this:
A. Shock, fire, and freeze resistance. (These statuses can wreck you, no matter how much damage protection you have.)
B. Normal, elemental, and shadow protection. (Player tests suggest that damage protection has less practical benefit than you might think.)
C. Piercing protection and poison resistance. (Piercing monsters include slimes, which are moderately hard, and beasts, which are easy. Shadow and elemental monsters are generally more difficult and more common in the late stages of the game.)
D. Stun and curse resistance.
What about offense? If you are a risk-taker or an expert player, then you should prioritize offensive bonuses before A, and use armor such as Chaos and Black Kat. If you are risk-averse or have a weak computer or network connection, then you should prioritize offensive bonuses between A and B, and use armor such as Wolver, Gunslinger/Padded, and Demo. If that is still too dangerous for you, then you should work on your skill, but you might also consider truly defensive armors such as Grey Feather and Dread Skelly.