Good on your for making the switch to SIPs!
I would say no to the peat and aeration. In the past I used bagged soil and OSF. Just use your Coots mix with 1 cup OSF per cu foot. I top dress 3ish times with Crustacean meal, Insect Frass, ground Barley, EWC, Compost, and lastly some Kashi. Once when I’m setting up the sip, once at planting and the last one at flip. Think of your sip as an engine, with the soil being the gas tank. You only have 15 gal tank, so don’t veg too long. Topdress will only carry you so far after your soil is depleted. Yes to EWC!
I keep my res full throughout the life of the grow, from the initial setup to close to harvest. I want the soil to have saturated, promote breakdown, and the life to get moving.
Are you using a microbial inoculate like em1, LABs or photosynthesis +? If not, I would give it a try! Bacterially dominate bottom, fungal dominate top, with a party in the middle!
If you haven’t already, check out Greens Probiotic thread on here. It’s the model I followed from the start and is a great jumping off point.
Hope this helps! If I didn’t answer your question, just ask. I am in the throughs of a hippy speedball (French Roast and Sunshine Queen) and haven’t balanced out yet. So I might just be rambling. Ha!