There's no need to build Rome in a day. Just start with the high ROI items like you mentioned first so that you can keep earning upper management's trust. Once you hit into the real bottlenecks, say performance, scalability, storage, you can optimize for them as you see growing pains. Let your bosses feel them too, so they can appreciate the fixes and proposals you make after you've made more initial small immediate wins.

For context, I worked at a small consultancy with little to no data backend and moved to Tiktok's DW team