Ended up booking some tickets through an agency to avoid the chance of finding the trains fully booked on arrival. Since the tickets are not very expensive the fees doubled the price from $30 r/t to $60 r/t, but that's still much cheaper than most countries. Our first choice at 14:07 was fully booked, but luckily someone else cancelled their tickets so we got the remaining seats. Got our visas yesterday as well, so we're all set ^