Ok, in general you are right, that "would" most of the times is used when talking about the past not the future. But in conditional clauses it can sometimes mean a future action as well. Ex. "I would never do that" can refer to the past and the future. "If I asked you, would you come?" again talking about the future action.
"I always bought eleven lemons" is a perfectly good English sentence, but I think it would primarily be used in a context where you're saying when you always bought the lemons. As in: "I used to go to that store over there, and whenever I did, I always bought eleven lemons."
All that said, I feel much better translating "zawsze kupowałem" as "I always used to buy" than as "I always bought".