Let's start at the end and work backwards. If you're getting zero, there's no point in adding more DI, unless you just want to change it less often (but change more each time you do). So, it's a wash.
There's no point in adding another membrane, unless you want a higher flow rate and/or better reject ratio, which you probably don't, since you haven't asked (and it's generally not worth the complication anyways).
There's no point in adding another carbon stage - if you somehow needed one, you'd probably know by now. The big thing carbon helps with is removing chlorine, and unless you have either A LOT in your source, or you're pushing a very high flow rate (multiple membranes), adding another carbon block isn't going to do squat for your water quality or membrane life. I know it's starting to get popular for people to run two carbon prefilters, but I feel like that's at least as much a marketing push by the vendors as it is justified. I'd love to see some testing done on the pre-membrane water for people who feel like they need one. Is there actually anything harmful left after just one stage?
Similarly, adding more sediment filters can make sense if you know for sure that you need them, but if you don't need them, you're either wasting money, or reducing performance (adding several, or really fine, sediment filters can drop pressure at the membrane enough that membrane performance suffers).
So, yes, generally - unless you're chasing a specific known problem (which it sounds like you aren't), don't change anything.
