What's the highest level a weapon/armor can be upgraded to? (i.e. Flawless, Epic, etc.)

"legendary" is the highest description. but you can upgrade weapons/armor way past legendary

Oh. How much more can you upgrade them?

How?

if you make fortify smithing and fortify enchanting potions, you can drink the fortify enchanting potion to fashion a boosted fortify smithing piece of armor, and wear those armors to upgrade your weapons at the smithing stations while drinking fortify smithing potions...

its like inception with boosts within boosts. you can look it up on the wikis to find out exactly how, but it ups your smithing a significant amount (like approx level 450 i think) and also your enchanting quite high as well

You don't want to know. Really. you don't.

It'll break your game. You'll be able to one-hit-kill anything.

its only fun if you've already finished the main quest and want to mess around

I did that once, but I only used ebony and didn`t overdo it so it didn`t broke my game.