These are perfectly reasonable questions. You should ask them of others and think about them yourself.
If I were you I’d buy new. $5K to $6K is an 18% difference, but dropping to $5K you also lose your warranty and your assurance that the bike hasn’t been shot to high hell. Other things to consider:
1) This is your first bike. You won’t be able to discern some problems right away by simple virtue of having nothing to compare to. Having no warranty makes that trickier.
2) Unless I’m mistaken, you’re no mechanic. While what SantaCruzRider says is true, it’s mostly true only for somebody who either has the hook-up or who works on their own bike. A couple of costly issues can easily rocket a used bike above a new bike’s price if you’re paying somebody else to fix them.
3) Break-in restrictions are good for you. If you have the willpower to adhere to them, they will force you to stay within your limits when you first get going.