kinda fail to see how real world coordinates screw things up… without using a real world based geometry system you completly screw up any scale that you have within a composited scene. Imagine taking the Cave Troll in LOTR and simply making him however you please, as much as you want to play with camera angles and zoom on him, you’re now screwing with your footage and distorting the realism.
As far as cloth and dynamics, they perform far better at a world scale than at a micro scale.
When animating, what does real world scale have to do with your keyframes? Your control rig is going to be zeroed out regardless and you might have a few extra degrees of movement here and there. If anything this data is far easier to edit and work with as you’re looking at a proper scale model and can interpret the data across your live action reference and other things.
back on topic…
keep your unit size to cm’s, when you start getting into feet you begin to have rounding values unless you want to use a decimal value of 4 (plus, it’s just a pain in the ass trying to look at a prop and realize that it’s 0.2353ft tall). Cm’s give you a nice precision when working to scale and also provide a solid grounds to base your dynamics & simulations off of.
as far as your importing goes, if you import a cm based object into a ft based environment then your object will default to being 0.13 units… not a very fun value to work with by any means. Keep it at cm’s and standardize yourself to use this workflow, you’ll notice it in almost every production facility you enter