You want to plan your set long before you get to the 4-star stage. I recommend that people read the wiki, select the 5-star loadout they want, and only then look back in the alchemy paths, to figure out how to get it.

Even though you are 4-star, it is not too late to change your alchemy paths. More than half of the cost of making a 5-star item comes in the final upgrade from 4-star to 5-star. Yes, it's that expensive. So don't throw good money after bad.

Lots of people choose their armor based on cosmetics. But keep in mind that you can wear a costume over your real armor. So this is no reason not to get ideal armor.

Divine and Grey Feather are strong defensive armors. In Tier 3, even the most defensive armor lets through tons of damage. So you can't rely on your armor; you have to dodge and kill quickly. For this reason, most players select armor that gives strong offensive bonuses. The Chaos upgrade would give you stronger offense. As Zeddy said, Divine Veil with Skolver Coat is one of the best general-purpose sets.

In your swords, you should forget about your Calibur, and replace it with a shadow sword. You might find my sword guide useful.

I have not answered your specific question about the order in which to upgrade. That's because the order doesn't matter much. But I would probably pick Skolver Coat (because you're nowhere near it yet) and Divine Veil (to get some shadow protection).

I have a question its, why are you saying he should get a grey feather mantle where at FSC is the same as Vog without the ASI with swords? So I think he should get all Divine because it has fire and shadow defense which makes it the best set for FSC.

If it were just a matter of one or the other, I'd agree that Vog is better. But bearing in mind that the OP is on a budget, the question is not which is better, but which is better for the cost. Is it worth making a fresh 5* for Sword ASI Med? If it were sword damage, I might (okay, I would) say yes. But for ASI, I don't think so. Even an unimproved DA is quick enough vs. zombies.

The Shock is really just a bonus, albeit a very significant one for those levels where it comes into play.

Throw in the fact that everyone wants costumes eventually, and Grey Feather looks (IMO) rather good, and the decision (for me) is sealed.

I also want to emphasise that my original post was more concerned with the question of GFM vs. Chaos Cowl--where I think the gulf (for the average player) is even wider, although the cost gap doesn't exist there--and GFM vs Skolver, which I'd be against for the reason of being non-FSC-viable.

Your viewpoint is reasonable too, of course.