Learn Hardcore Japanese: sorede, eki de koohii wo kaimasita.

Japanese often omits the subject when it’s clear from context. The sentence simply states the action: “(I) bought coffee at the station.” If you need to make the subject explicit, you can add 私は: 私は駅でコーヒーを買いました. Avoid overusing 私 in natural conversation.

Why is the particle で used after 駅? What’s the difference between で and に here?

Use で to mark the place where an action happens. Buying is an action done at a location, so 駅で is correct. に marks a point in time, existence, or a destination/arrival.

駅に着きました (arrived at the station) → destination/arrival
駅に人がいます (there are people at the station) → existence Not: × 駅にコーヒーを買いました.

Can I change the word order? For example, コーヒーを駅で買いました vs. 駅でコーヒーを買いました.

Yes. Particles carry the roles, so both are fine as long as the verb stays at the end.

駅でコーヒーを買いました (slight emphasis on where)
コーヒーを駅で買いました (slight emphasis on what) For stronger contrast/topic, use は: コーヒーは駅で買いました / 駅ではコーヒーを買いました.

What does それで do here? How is it different from だから, それから, そして, and それに?

それで links to the previous sentence as “so/and then,” often implying a result or continuation.