Meadow said "Is UP express pretty accessible in the airport?
Do you know whether I can purchase the go train ticket when I get there? How about ticket for UP express? I worry that if I purchase tickets in advance with possible flight delays I will loose those tickets "
It is, there are signs at the airport telling you where the UP Express is. You can purchase Go Train tickets on your phone/online. Whoever on the train would just check the ticket on your phone but they never did when I was there last year. I purchased the all-day pass or something like that. There are also kiosk machines at the train station.