A few points to start with:
First, what is your budget? You're going to be limited in what boats and what size boats are possible depending on the finances.
Second, when you say a total crew of 6–8, is that 6–8 separate individuals, four couples, a couple and several friends, etc? This can make a difference in the size boat you need, since four couples can get away with four double berths, 6–8 separate individuals, usually won't be too happy with sharing berths on a longer voyage like that—meaning that you'd need 6–8 berths.
Third, what kind of sailing experience do you and your friend have? How much experience does the rest of the people you're looking to have as crew have among them? My guess is that you don't have much, based on the questions you're asking.
There have been many posts, mostly by Jeff_H, regarding the pros and cons of the different sailplans. You'd do well to search them out. I'd highly recommend you read this
POST to help you get the most out of sailnet, as well as learn how to search the Sailnet forums using google, since the sailnet search function is somewhat limited.
There are a lot of boats that would be suitable for this type of voyage, but a lot of what is suitable for you and your crew depends on what you're looking to get out of the voyage and what your longer term plans for the boat are.