What you need is money, more than you can imagine. And then, time. More than you think of that as well. You also need to get a suitable boat, fit her out to proper seaworthy standards, and learn how to sail her and - very important - be reasonably self sufficient.
What a suitable boat is, is very individual when it comes to size and standard, but she has to be a proper oceangoing sailing boat. People sail the world in all kinds of boats from 22 ft to sea going luxury insanity.
Start by crewing in the local harbour or take some sailing classes to see how you like it before buying a boat - or crew on a transatlantic or something like this. Read "the voyagers handbook" by Beth Leonard, 2nd edition. HIGHLY RECCOMENDED!
More specifically when it comes to time and effort; once the boat is in you hand, and money is in order, you need a very focused year to get shipshape mentally (and physically) and to get the boat ready to go.
Livingcosts: 8-10000 usd a year can take you a long way. People get by for less, but some need more. All depending on where you go, how you go, and you need of comforts.
Boats: take a peep at yachtworld.com, filter "cruiser" and 28-35 ft, (good size for 2-3 on board) and start looking at boats from the 70´s. 70´s gpr boats are usually very strong and seagoing boats. And quite cheap.
For keeping up boat underway: about 10-20% of the boats worth will be what you need to maintain her at all times. We spent 25% of our living costs while underway, including investments.
