In order to build trust with stakeholders during your first 6-12 months, aim to deliver wins for the business and get your name associated with the deliverables you work on.
Train internal stakeholders on how to use and interpret data and model workings so you can have champions outside of the data science function that can advocate for your team.
It's key for a data science team to have a very good dev team that can offer support by suggesting the right tools and the right architecture that you need as you go.
When balancing long-term vision and short-term goals, you need to plan the roadmap for your long-term version by making your “grocery list” of needs to get there, while in the short-term you need to ask questions like, “What do I have now and what can I do with it?” and you need to talk with your internal stakeholders to learn and understand the priorities of the business. Identify the immediate pain points that you can provide a solution for, compare them to your long-term needs, and utilize any overlapping needs to move you simultaneously closer to both.
An easy way to extract small wins as a new data leader is to approach internal stakeholders and ask them about the data sets they use in their day-to-day work and how they use them. Once you understand what, why, and how they are using them, you can offer your expertise to make their job easier, whether by automating the way they access and organize their data sets, or by teaching them to use their data in a more efficient way. By doing that, you will quickly gain understanding of how the organization is using data, which data is usable, and you will have a use case. When you solve these problems, you will also start building up your sponsors, the champions who support your team within the larger organization.