Unless there is a call from the context for a particular verb aspect, I would use simple past for all of these.

For the first sentence both could be correct but I'm guessing the latter "used to buy" would be more appropriate. It means that it is a habitual action that was done over time not just in one instance. If you say "bought" it tends to mean that he bought them all at once. The answer to the second sentence is 2. When you have two past actions and one happens before the other, the action that happens before must be in the past perfect tense "had".