I am doing the same thing.
First, you have to learn how to access the api if you dont know how (httr::get()).
Second, do your data processing in separate scripts (especially if you have a LOT of cleaning to do)
Then finally create a shiny app.
Unless you have your own server, I strongly suggest against displaying your data in real time. I am doing the same thing as you and the get requests takes a while to load (more than 2 sec) which will make your webapp feel less snappy. You can save your data in a cache using saveRDS() and ?readRDS() so your app wont have to make a get request every single time.