>>713839538
Your armour and shield are what matter most, and don't bother with putting points in health. The Terraria dungeon has two crystal hearts that respawn (and follow your world's Gatherable Objects settings) that you can use to increase it a lot. I'm not sure what the limit is on them, if there is one.

>>713839918
There's a few Hardmode mobs and also the Moon Lord, it's honestly more than I was expecting.