questions about tours and hostels (Istanbul)

hi, i have been travelling through europe for two months now. I am 90% coming to istanbul this week. i have looked on hostelworld.com and seen excellent ratings for a few hostels.. on is called Bauhaus. Does anyone have any experience with these? They seem to be in the old part of the city. Is that good?

do you think it is necessary to book ahead for a group tour of Turkey or is it easy to join from there... ? I had called Fez travel. They were nice... but I saw much better deals through hostelworld. One never knows, though. Sometimes you get a good deal, and sometimes "you get what you pay for"! I saw this at around Protected content do you think? Protected content

Any opinions would be appreciated!

Best,
Felice