My experience differs...
I find white sugar to be easier to measure, (my tank takes two packets of sugar for maintence which is pretty rad it worked out like that) and I can add it all at once without the same consequence to the pH.
Your tank sounds like it will work. I would personally be leary about using that skimmer if you can not get it to return to the back chamber. You might consider a smaller more appropriately sized skimmer like some of the options from nano tuners or other similar companies. Ya the bigger skimmer the better, but at some point it is just overkill. At one pair of erectus your really not going to have that high of a bioload.
I would encourage you to go with naussarius snails, cerith snails, and netrite snails. The others will mow down the red macro's you desire. IME these are good choices. If your going to let your tank mature as you have stated you will most likely see a surge of stomella snails which are also good. I would feed the tank starting with a little and gradually increasing to the full day of seahorse feeding a few weeks before getting the seahorses. This will let the micro fauna mature and the bacteria population grow. If you are having algae problems during this period it is a lot easier to deal with then if the tank is stocked (just turn off the lights for a bit, run that skimmer, and then do a water change).
Good Luck.
HTH
