Transplanting a seedling into SIP, or transplanting anything into SIP from NON-SIP setup will, 95% of the time, experience a two-week growth stall-out that can sometimes freak people out the first time. The work-around I use is a mini-SIP seedling/clone system so they are acclimatized to the constant moisture gradient, high oxygenation. This is very effective if you choose to keep using SIP I would be happy to discuss and illustrate. Others simply plant in full SIP.
The air gap below is the key and SIPs grow massive biomass as result of not wasting their energy constantly adapting to the deluge and dry-out that the traditional container growing system puts them through. Slow motion footage of SIP Cannabis show a plant constantly growing at a steady rate... and the same footage of trad container grows always shows a growth burst for 1-2 days after watering, then nothing for days and days until the next watering.
Be careful when you start getting ideas of putting air injection via pumps into reservoirs, pH can be issue - depending your h2o source of course - but in addition, unless you place on a timer and run only 30 sec. bursts every 10 minutes, you will start growing massive DWT-style roots in your reservoir as I have done with many an experiment. Now I have to care for the rez as though its a DWT, which wasn't the plan. When on burst pumps make can make a great addition. However, leave on 100% and you get more roots than you might have bargained for.... as I have on a current plant, only because I forgot to set the pump! Doh! I have a large rez (9+gal) under a 7 gallon nursery pot in this case so there is lots of room - but now I'm scared they will dry-out if I let level drop as air gap can expand to 10 inches as level drops. Root mass doesn't explode like this when in identical conditions with pumps only on short burst timers (they can help prevent any sediment that comes through from becoming anaerobic, but not necc for careful gardeners).
Typically I run 2x 10gal soft pots inside 27gal tote SIPs that have only 5-6 gal. rez between the two plants. Or outdoors I do without the soft pots and fill the tote. False floors are created either with a second tote (find a brand that has 27 gal and 17 gal in same footprint, then stack) or by cutting the lid down and propping up with vertically placed PVC pipe or something strong that takes least amount of space so rez is decent size.
Drilling out as many holes as you can in the floor is very beneficial, and you must line with a synthetic fabric, as cotton t-shirt or the like will not even last 2 months, guaranteed. Also, aerate that soil. Sorry if you hate perlite but love SIPs because there's nothing like it, although I constantly try to find a replacement, SIPs and perlite are like peanut butter and jelly, once they find each other they seem as though made for each other. It sucks to lose a beautiful 13-week flowering Sativa to root rot suddenly in week 11, but is exactly what will happen if not enough aeration. It's a "f^$&-around and find-out" scenario and painful in the extreme. With 30%, by volume, perlite, it's guaranteed you'll have no problems.
I recommend to make plastic covers as mulch, especially if topdressing, especially outdoors (to keep heavy rain from leaching bio-material into the reservoir which may putrify), and especially if doing TLO/LOS to maximize soil-use. It just work's the best, and is very simple. If doing soilless indoors you can go without and have a completely dry top 2 centimetres so as to manage fungus gnats if that's an issue.
Fertigating with GH Maxi, GH Flora 3pt. or GH Lucas works well, also I use MegaCrop 2 part as fertigation in soilless SIPs (I don't like the synthetic chelates so much and MC uses Amino chelates), and I mix to 75% of maximum recommended strength, max. Grow Dots from Real Growers are the go-to time-release ferts, use as instructed, and their microbe package is excellent, though I also recommend NPK's microbes also as they split into grow and flower, giving you something like 5 phosphate solubilizing species in the Flower package, and 4-5 endo-mycorrhizal species in the Grow package accompanied by, I believe, Trichoderma and other common beneficial bacteria. Both really work well and give you awesome control when growing God-style, or any style.
If going fertigated soilless, do make sure you are using well-buffered peat, store-bought SS#4,
ProMix, or buffered coco. This passive method can hit you with a toxicity or even develop actual salt lines if you allow multiple dry backs early-on or over feed (so don't, until the end, then you may drought to your heart's content to make stronger weed, just realize it takes an extra week, compared to traditional container growing, just to dry out the SIP.)
These are most of the SIP questions I'm usually asked on the other forums, neighbours, etc. I hope its ok I dumped them all upon you!
Best regards.
Slava Ukraini!