Advice for postdoc application
The best answer may depend on what other questions are asked on the application form. These types of questions are usually used to assess whether you have a clear research line moving forward, but it is also helpful to know how you are going to break your research line into smaller goals. This is typical for grant applications -- high level research questions followed by measurable research activities.

So, if the 650 words gives you space, I would suggest providing both answers. The high-level research questions you want to answer and the first few research activities that will support this.

I wouldn't spend too much time talking about general service activities such as reviewing papers, but organizing a workshop to support those working in your research area would be worth mentioning, as this demonstrates broader impact.



After the edit:

As I suspected, the other questions are related to the first question you asked about. So, my overall advice doesn't change, but you can spread the answers across your questions as appropriate.

For instance, what you hope to achieve is related to the planned activities, but is looking for a broader answer - here is where you can talk about the expected impact of your work on the field.

In your dissertation or present research summary you can introduce some of the higher-level questions being answered, leaving more space to talk about specific activities in the response to that question.