Sounds great, and I think for the food thing that there should be a bar in the stamina/fatigue bar that would either make it increase very slowly if you haven't ate for a long time, or would have a cap that is steadily declining as you don't eat food or sleep. And as for making it optional, I don't think so, I mean what is the point? If people are really annoyed they could mod it out, but I understand why people wouldn't want the game to turn into the Sims or something, but they could have the effects somewhat subtle so they only had to eat or sleep every 2-3 days or something. Also, I think it would be cool for inventory to be shown on your character, at least for things like your money pouch, and I think it would be cool to have a flask for water (or other liquids) that you could fill at a stream or something.
WOW, you just gave me the BEST idea ever!
Let's say you get water in a flask from a river, then use alchemy to combine the flask with a potion with damage health attribute, so if an NPC is about to starve or die from thirst, you say "here have some water." then they will die! This can provide for some sneaky Dark Brotherhood quests, which involve you first stealing the NPC's food, then giving the poisoned flask. Or, Maybe you need to slip a "Silence" potion into someone's flask before they fight your group (like if the fighter's guild is fighting a mage's guild. This can be EXPANDED to the point where you can poision the enemy team in a Arena! Giving you an easy win/easy gold from a bet.