Does higher bid at tax auction decrease likelyhood of redemption?

[Tom MacDonald]

A few questions about tax foreclosures that I'm hoping the BP community can help answer.  I'll be bidding in Texas but I suspect these are general questions: 

1. If the minimum bid is $5000, does this mean that the homeowner owes exactly $5000 in back taxes?
2. If the winning bid on this property ends up being $11250, who keeps the additional $6250?
3. If the answer to #2 is the homeowner (let's call him George), does this mean that George will likely just turn around and use the $6250 ($5000 taxes plus 25% redemption premium) to redeem the property from the winner of the auction?
4. If George has $100,000 left on his mortgage when the property is sold at the tax auction for $11250, who is responsible for that mortgage payment?

Thanks ya'll!
Tom