I don't know about other "orchid food" that promotes root growth, perhaps you can tell us the brand and information so we can help you figure that out. Kelp Max is not so much a "food" as a stimulant for root growth and plant vitality. I ordered mine online, but since then I have seen it in a store that sells to organic gardeners and hydroponic type stuff. You might do an online search for hydroponic garden stores or something like that, maybe a local nursery. Big box stores probably won't carry it in a normal garden center. People have good luck with Superthrive too. I haven't tried it yet.

I would not put them back in moss - the tightly packed moss method is designed for specific greenhouse growing circumstances and rarely works in the home. There isn't enough air, it doesn't dry out enough. I do use coarse bark with some sphagnum moss in it (maybe 1/4 of the mix) to keep some moisture at the roots. I do the moss because I tend to under water and it is very dry here. The roots you have now will not thrive under new conditions, they were adapted to the greenhouse and moss, however you can hope to support the plant until new roots grow that are adapted to your conditions.

I don't know about leaving the roots above ground, but misting shouldn't get the foliage wet, just damp. Just mist the roots, a small amount on the leaves should dry right up. It might depend on your humidity, the time of day, air movement, etc.