couple newbie questions

First of all just started playing a week ago and am LOVING it. Have a couple questions about the game. Just an FYI i am not able to spend real money on the game so anything that i need real money for will not help.
1. what happens if you don't feed your horse? If it's ok how long can they go without food? what happens if they are like starving? 
2. do the horses actually need tack for anything? 
3. what kind of things are good to sell for extra money?

Any other suggestions would be greatly appreciated.
thanks

1. They'll die after 9 days.
2. They don't necessarily need tack, especially if you're not Showing, but tack gives bonus stat points based on the grade and speciality of tack.
3. Anything you don't want or need anymore can be traded in in General Store.

Check the Help section or Game Guides in Forums for lots of useful info!