Thanks for all the input from everyone. I just had a chance to catch up with this thread and it's given me a ton to think about. I've been spending a bunch of time over on RC reading about skimmerless systems and also the pros of skimmers. I don't know anything about anything, really. So many different systems can work. My feeling is that if I'm going to run carbon (which I always do), and possibly purigen or chemi-pure, than I'm already messing up the natural flow of things in my reef. So adding in a skimmer, which the best ones only pull 30% or so of stuff from the water, isn't going to make much more of a difference and they do oxygenate and can save you, just like carbon, if contaminants enter the water (I do have a toddler). I didn't ever mean for this to be about skimmer vs no skimmer, because I may very well use one, more of that I don't need to consider room for one in the sump. The discussion sure got me thinking though, so I appreciate it!
Another thing I realized is I haven't thought of the sump at all as a place for nutrient removal. My main idea for the sump, besides not having equipment hanging on the tank, was for diversity. It excites me to think of creating another area for creatures to live that may not in the dt, like in a dsb or a cryptic zone. I think that the more diverse the life in the system, the more stable it'll be for me. And more interesting too. That's the microbiologist in me.
I need to think about nutrient export and I need to look into the maintenance and risks of each of the options.
And I need to start making some decisions of what I want to keep in the tank! That's a tough one because I want to keep it all