Nice setup you will have plenty pf places to mount your colonies.
You really shouldn't need a skimmer for anything smaller than 40g though. As long as you have good filtration/surface flow, do weekly water changes, keep the sand bed clean, and run something like Purigen or ChemiPure Blue the organics should not be an issue.
On mine I do about a 15% water change every week and vac the sand bed once a month and everything is doing really well. I'm running a 306 with 1/2 coarse Bio-Home ultimate media in the bottom two trays, with 2 pouches of ChemiPure elite, and 2 100ml bags of Purigen on the top tray. the ChemiPure is replaced every 6 weeks and I swap out and regen the Purigen pouches every 2 months weather they need it or not.
Running that setup my levels stay really stable overall with Sal 1.021, alk at 11-12 dkh, ph at 8.1, cal 420. Ammonia at 0, Nitrite 0, Nitrates .25-.5 depending on the kit, and phos 0 -.025. I dose with SeaChem Trace twice a week and Kent Mg three-four times a week to maintain 1400ppm. That's what I'm doing on my 40 and have seen really solid growth with my zoas. In the past 2-3 months 4 of my colonies have taken off like weeds. All but one colony has shown very rapid growth with multiple new heads over the past three months since adding them.