Its not the size that determines suitability it is the construction. There are lots of folks who circumnavigate/cruise in boats that are smaller than 35 feet. Some do it in boats under 30.
As to how to tell if something is majorly wrong, Sailingdog
wrote out a very thoughtful and helpful thread here : http://www.sailnet.com/forums/buying...trip-tips.html
Spend the money for a really thorough, qualified surveyor. Yes, they are expensive until you realize that the $1,000 you just spent saved you almost $50,000 in boat repairs.Then their service becomes "cheap as chips".
Also, spend us much time sailing on OPB's as you can. It will not only improve your sailing skills but will give you an idea of what you want in a boat.
Lastly, take your time. Buying a boat can be a long process. We've been at it for 2 years and are still looking...