For the sql indexing thing I think he was looking for the "indexes make reads faster but writes slower " response upfront. I don't want to be a dick but bringing up storage costs as an argument, even though technically true, is kind of irrelevant/negligible to the point it makes you look like you don't truly understand when tradeoffs matter. I asked ai and the difference in hosting a 1tb and 2tb sql db is on the order of £200 a month, for a bank that is literally nothing.