if you have only carry on there should be no issue getting on the bus. if you have a large suitcase, the bus driver will use his discretion re: allowing on the bus.
the bus will go to the center of o'stad. choose a bus that says "oranjestad or downtown"
when leaving the airport...go straight out the main exit door and walk straight thru the parking lot and follow the cars exiting toward San Nic. (rotary)
per the photo continue about 100 yds and the bus stop will be on the left.
be careful as i do not know if there are sidewalks. the road that the bus stop is on is considered a highway.
i recommend a taxi to downtown for convenience and safety. crossing the highway could be treacherous.