Types of Train ticket and obtaining them at Glasgow airport

My wife and I will be flying into Glasgow Airport from Iceland around 11 am on Sunday June 16. We wish to travel to Sunderland by train that same day. We plan to return to stay in Glasgow city overnight on Monday July 1 in order to take our flight back to Iceland from Glasgow airport leaving at 2 pm on Tuesday July 2. It appears to me that purchasing a super off peak ticket with an open return before we leave for our trip would be the best alternative as I think that it would allow us to travel on a variety of trains from Glasgow airport to Sunderland on June 16 even if our plane was delayed by a few hours but still arrived the same day. Am I correct in this or would I have to specify a particular train time to leave Glasgow airport and would I lose the ticket if we could not make that train? I know that we need to take the bus from Glasgow airport to the train (all included in the ticket price) but wonder as we live in Canada how we can pick up the ticket at Glasgow airport or are e tickets available? Thanks

A superoffpeak ticket can be bought on the day - there is no discount for buying in advance. It's valid on any superoffpeak train on the day of outward travel and similarly return within a month.

I don't know if there is anywhere at Glasgow Airport to pick a prebooked ticket up - I very much suspect not. You'd need to pay for the bus ticket to the station.

No e tickets on this route

Looking at:
http://www.eastcoast.co.uk/
(the train site I always use) it appears cheaper to buy a separate ticket from the airport to Glasgow and then another from there. The route takes you by bus to Paisley station and then train to Glasgow, An alternative is a direct shuttle bus to Glasgow every 10 minutes and quicker than the bus/train alternative. Using Eastcoast you can state that you want to pick up your ticket at an automatic ticket machine at Glasgow. You will need the credit card with which you booked the tickets.
Should you buy an off peak return or book in advance. You pays your money and takes your chance. Personally I would go for a train from Glasgow Central/Queen Street at least 5 hrs after scheduled touch down.

There is no station at Glasgow airport, the nearest would be Paisley.

[http://www.visitscotland.com/travel/around-scotland/train]