Try to get silk, preferably silkworms, the process of creating the insects and then making the silk is not that complicated considering the conditions of the mc. Silk is an excellent material for the internal lining of armor, as well as a great material for clothing and bed sheets and things like that. Then use the leather using thin metal plates covered in rubber, glue them in one layer and then place another layer on top, if done well it will be light armor with excellent protection. If you can make some material with a similar effect to Kevlar that would be great. It would be something like this, just add a layer of leather or something similar to Kevlar on top.
Like most attacks in the medieval era, they were simple frontal attacks, all he had to do was give each soldier a throwable potion of poison, And when the enemy army got close, they would throw the potions, thus poisoning most of the enemy army. Or simply use a potion of strength 2, a potion of speed 2, haste 2, and eat an enchanted golden apple and eliminate all enemies alone.