Welcome to Slippertalk from Montreal Canada. A smallish greenhouse will soon be quite crowded. So many wonderful plants out there, too little room.
I grow plants with few or no roots in straight New Zealand sphagnum moss. This works for bare root plants as well. I use leca in the bottom of the pot for aeration then use the sphagnum around the roots and to fill the pot. The sphagnum has been soaked in water for several hours then squeezed to remove most of the water, leaving moist but not soggy moss. I do pack the moss around the plant so it is firm but not tightly packed and do not "fluff" up the moss as some youtube orchid growers suggest--I find "fluffed" moss dries out too quickly in my home environment and I need to water quite frequently. I use small pots (usually regular green pots, now trying clear plastic pots with slits or holes). I cover the potted up plants with a clear plastic dome to increase the humidity in the orchid ICU. I keep the moss moist but not soggy, watering as needed--I do not let it dry out. I grow the rest of my plants under LED lights. The plants in ICU are not under lights until I see new root tips from the cattleya/oncidium/phal hybrids or new leaf growth on the paphs. Once the root tips or new leaves are big enough, I move the plant into the light garden. I had purchased 2 paph seedlings with 4" leaf span, in May 2024. They came bare root and each had 2 viable roots. They stayed under the dome, growing in the moss for 3 months, watered with room temperature tap water, no fertilizer. Then, I repotted into a seedling paph mix once the new leaf was about 1" in size. They continue to produce a new leaf around every 3 months and each leaf is bigger than the previous leaf. I have never used live sphagnum moss but it sounds like an even better option if available.
This system works for me and I have bought around 35% of my plants bare root. I have not tried this method with other types of sphagnum moss. If you decided to give it a try, you may need to adapt it to your growing environment as your humidity may be much higher in a greenhouse.
