Have a look at osmotics website and if you get stuck email them, there very helpful.
As far as I know the prefilters and membranes are a universal size.
Sediment, carbon, membrane and di resin/polishing cart. That is how you want it, replacing the di resin with a carbon filter is not a very good idea, after the membrane you will still have about 15 tds depending on your setup, the di resin brings that down to 0 tds, ideally you want a inline tds meter after the membrane and after the di pod to make sure it’s zero after the di and change the resin as soon as it goes to 1 tds.
A carbon filter after the membrane will do next to nothing.
That’s fine with the softener feeding it, it will lengthen the life of you membrane slightly, only downside is you will get through more softener salt.