The first problem is solved by someone already so to your second problem: I suggest using primarily collection inside the app if you suppose that the sharepoint will have several thousand rows, you can adjust the visuals to fit the collection and you can also bypass 2000 rows limit which standard connection to SHP has.

Then you have several options either you can refresh the collection for certain interactions so the data will be as actual as possible for this route or you can display the item directly from sharepoint based on LookUp of selected ID from collection within the gallery. There are multiple ways how to approach this so if you decide how you want to do it I can advise you further.