Dave
I would recommend flying into Baltimore/BWI and then make a connection
for the commuter flight to Ocean City, MD. It was just announced that a
company has started making daily flights from BWI to Ocean City, I believe
flight time BWI to O.C. is 40 min or so.
If Greyhound is your choice, still fly into BWI then take ground
transportation to Baltimore(20 miles) and from there take Greyhound to O.C.
I can not say as to how full the busses are but I would say that you should
not have a problem except if you are traveling on a Friday Afternoon. I
haven't had to travel by buss since I was in the military 40 years ago.
If you flew into New York you would still have to get to Baltimore(250
miles+-) and then take Greyhound from Baltimore to O.C. Adding additional
time and expense

As to your VISA card I would suggest checking with the company that issued
your card, and be sure to ask about their currency conversion fees/rates.

I hope this helps

Frank