I know that anything is playable, but I don't want to have a character that dies every few fights.

My character is going to be a breton Sword/shield fighter. I never got past how unrealistic it would be for an adventurer to wear heavy armor 24/7, so I'm going to make him wear light armor.

Would this be a decent build? 1hand, light armor, block, archery, smithing would be my main ones.

you wont have any problems at all with smithing and the perks for light armor you can get high armor no problem, or even get to the armor cap, the only difference between heavy and light armor is that with light getting to the armor cap takes a little bit more time its more about roleplay and personal preference

With decent smithing and a little bit of training, any kind of armour can provide enough armour rating to hit the 80% damage reduction cap (Around 570-600ish AR). So light armour is perfectly viable in the long run, if not better (Since the additional stamina regenration allows for more shield slams or power attacks)

My highest toon is an argonion at 33. He is in light dragon armor and uses a shield. He wrecks house till he meets a mage. But I do have spellbreaker for that. The only other time I had to change tactic was liars retreat. At 32 about 8 falmer attack me at once. I just went back with a pair of flawless ebony axes with absorb health on them. Slice and diced falmer anyone?