Glad to hear you are doing your due diligence and hopefully this site helps out. To answer your second question: Typically as the borrow rate increases it makes it more expensive to keep or start a new short position, making it less profitable to short the stock.

“An increase in stock borrow rates may force (squeeze) some short sellers into closing their positions – getting out to realize their remaining mark-to-market profits and exiting before other buy-to-covers drive the stock price up,” – S3 Partners analyst Ihor Dusaniwsky

As for what’s considered high, that relative to the volatility of the stock and how long one plans to hold the short position. When looking at the highest borrowing rate on iBorrowDesk.com there are stocks with over 100%, up to 412%.