Since you said you were wanting to feature the arms race of the guns fairly heavily, a few notes on that.
Any arms race is a constant struggle between Offense and Defense, and each one inevitably determines what you get from the other. Sword shapes were dictated by the armor they needed to defend against, which was often a matter of what could be safely worn/carried in that particular climate. The crusades make a good study of that, where the mid-eastern slashing swords couldn't get through the heavy plate and mail (being slashing weapons made to battle quilted cloth and leather armor) while the Europeans were slowing dieing from the heat of wearing pounds and pounds of steel in the desert.
When guns first came around to the Western civilizations, they didn't replace Swords, they replaced Bows and Arrows (or crossbows), but were still too inaccurate, slow to reload, and sensitive to moister. We're talking muskets. Armor was still a common thing. In fact, the term "bulletproof" was originally referring to a mark on a piece of armor left by a musket ball, which the smith would fire point blank at his product to prove that it could stop bullets. The major leaps in gun technology were:
Rifled Barrels - increased Range/accuracy significantly but were slow, expensive, and fragile, and did not work well with a muzzle-loading balls.
Conical Bullets - increased Range/accuracy dramatically, had hollow base that would expand to engage barrel rifling when fired, allowing muzzle loading without damaging the rifling.
Cartridge - Significantly simplified loading, increasing rate of fire. Allowed for Breach-loading design, birth of modern guns.
With the advent of the cartridge, various things like the revolvers you typically think of in westerns became possible. This was when the gun really started replacing swords as the primary killing tool, because it allowed you to fire multiple shots before an enemy had time to close the distance.
As these developments were going on Armor was becoming increasingly rare in for several reasons. It was far less effective in the face of gun developments, it was heavy and expensive to include in military standard issue and was phased out by the American civil war. As a result those who chose to wear it would face a stigma as cowards. Breastplates were in use in the early 19th century, but had been phased out by the end. Ballistic vests were experimented heavily, but weren't widely adopted until new materials and increased manufacturing capabilities made them practical in the early 20th century. However, armor adapted to stop high velocity bullets in free flight operate on different physical principles than that meant to stop wielded stabbing implements, which is a problem still being researched today. The most common solution is to simply layer the two types of armor together.
Not sure how you want to treat bullets for your magic guns (if you intend to have ammunition at all), but hopefully this will give you some ideas for the progression/stages of your arms race.