If I understand this, you havent seen this bike in person yet? If so, at least be realistic that even if good shape from not being used too much, its completely realistic that the remenants of the grease is original from the 80s, or the spokes aren't properly tensioned....I dont know how much bike mechanic stuff you do or are interested in, but its in your best interests to at least check or have someone check this stuff, as it could very well have implications on your trip

moral of that story, spending some money on checking/regreasing/adjusting would be well spent, and if not, could end up with costs during the trip.
That looks like a 50/40 and maybe a 28 at back. My first bike trip was on a bike of similar gearing, it might be ok for flat Yucatan, but that is pretty high gearing , so just be aware, and have shoes that are good for walking at times up hills.