1)While slideshow is running the watermark is not shown on pictures.
Is it normal?
Sure if your using on the fly and not permanent watermarking
2) please, can someone give me an example of an .htaccess for a folder with original images above the root?. http://www.photopost.com/tipsphp.html
3) Is there a solution to make google only hotlink the thumbs?
Not that I am aware of but this might be a question to ask them since this is a question about there service. If you prevent guests from viewing the large images by requiring people to be registered under admin => registration options you should keep them from viewing large images though
4) Is it normal some minute delay in updating information about how many pictures are in a category?
all depends what we are talking about here and where