A higher delay simply reduces the amount of frame advances you need to perform to hit a certain spread/frame. A lower delay is good because you can usually reliably hit the same seconds/delay on different seeds, while a higher delay is good because it reduces the amount of frame you need to advance by a significant amount.Encounter slots. Got it.
High delay vs high frame? I'm under the assumption a higher max frame gives you more spreads to choose from, and a higher delay is only needed if you want to change the year or something like that?
And ID finder seems to be for rng abusing id/sid. Does it help with finding shiny spreads for my current id/sid?
For finding shiny spreads, try useing the program PokéRNG, a link to which can be found on the first page of this thread.