When one changes the screen resolution in a retina iMac, will all resolutions look as crispy as the standard?
The other resolutions use non-integer scaling which (a) isn't quite as pin-sharp as the standard 2x mode and (b) puts some extra load on the GPU (but that's not a big issue on a model with a half-decent GPU).
However - all of those resolutions will look
much sharper than your non-retina display* in its native mode and
night-and-day better than your non-retina display trying to display a non-native resolution (which usually looks awful - if that's what you're worrying about, don't).
Can't guarantee anything for inDesign (the default res is just about the 'sweet spot' for most Mac software) but (unless Adobe have done anything daft like not properly supporting retina), one of the scaled modes should make the controls larger without the sort of blurriness that causes on standard def.
* E.g. the "looks like 1600x900" scaled resolution - the 'lowest' on offer without tweaks -
isn't 1600x900 - its 3200x1800 with double-sized text re-scaled to 5k (...in broad strokes. I've never seen a detailed description of how it works and its possible that MacOS is actually even smarter than that), so it starts off with more detail than your 1440p and, while the up-scaling to 5k creates a few 'artifacts' the 5k screen is fine enough to mostly hide them.