I am not going to pretent to be the know-all of boats. I will say there are people WAY more knowledgeable about them on this forum than I am - Jeff_H especially. Now, that being said...
I do not think a Beneteau or Bavaria would be my first choice of boats to cross the Atlantic with. I am not saying they cannot make it (you should see the junk people sail around in!!!), but you will really have to get creative with water, fuel, rigging, etc. They are not a "bad" boat and will likely be fine for the Med... but crossing the Atalantic? If that is very high on your importance list, try looking at some different boats. I personally like: Mason, Valiant, Bristol, Hylas (one of my favorites) to name a few. Jeff or others can provide a more detailed list, but any of those are good boats that can make a crossing. Better be ready to open up the checkbook though. In addition, any of those boats will likely need $$ to outfit it to make the crossing.
Here is another suggestion: If you want a Bene, or Jeauneau, or Bavaria, buy it. Use it in the Med. When you are ready to go across the Atlantic, put it on Dock Wise transport. Given the wear and tear and equipment you are going to buy, it might actually be cheaper. If you want to put on your list of accomplishments "Crossed the Big Pond", crew on a boat with a Captain for a delivery.
Also, I do not know how much offshore expereience you have, but I would really study up and crew with some others before hoping across the Atlantic.
Regarding new versus used, there are positives and negatives both ways I guess. There is nothing wrong with buying used... if you have a good survey. New boats DO HAVE PROBLEMS. New does not mean you are problem free until the warranty runs out. It just means someone else has to fix it for you and the parts are free. However, if you buy new: You know how the boat has been cared for. You know the maintenance. You know the boat has not been abused or a surveyor has not missed something. There are benefits to buying new. However, on a new boat, you will really drop some change into outfitting it - coastal or offshore.
Maintenance depends on how much you use the boat, but in general, larger boats will require more money for maintenance... but not as much as you think. I have owned: 25, 32, 38, and 40 foot boats. The 40 def costs more than the 25 in maintenance, but not as big of a difference b/t the 32 or 38. My opinion is to be conscious of your maintenance budget, but do not let that be the deciding factor.
People cross the Atlantic in boats smaller than 36 feet, however, in general, the longer the boat, the better off you are. My opinion is that a well built boat, properly outfitted, with an experienced crew, can cross the Atalantic safely at 36 feet... or even smaller. That being said: I would take a Hunter across the Atlantic with a knowledgeable, experienced crew before I would take a Valiant across with someone that has no or little offshore experience.
Just my thoughts and opinions. Fair winds and good luck in your search.
PS I have heard Croatia is beautiful sailing.