Im not an expert at growing orchids, but I did stay at a Holiday Inn last night. Ok, enough jokes. I have been doing a lot of reading on this board, other sites and a stack of books,I have a few orchids that I havent killed yet, so I am going to give you some answers that I think would be correct.
First, there are a hundred answers to every question based on what each person had done or would like to do. So dont be confused, just understand there are 100 ways to skin a cat.
For medium, there are a few things to keep in mind. The media need to drain well, meaning that when you pour water on the top it runs out the bottom fairly freely. The medium also needs to allow air flow to the roots. I dont think it needs to dry out, but that isnt the issue that you will be facing. The medium's ability to hold moisture I feel will be important to you because of your low humidity.
Check out the S/H (semi-hydroponic) section of this forum, I think it might be up your alley. Also a bark based medium is a good choice, but I would add some sphagnum moss for moisture retention. Read though the beginners discussion section, there are a lot of examples of mediums.
Fertlizer. Feed at every watering. You can start with a basic "orchid food" and follow the directions. Or you can opt to go with the more advanced foods such as MSU (do a search on this board). Or you can use a nutrient such as those sold for hydroponic systems. I use a product from General Hydroponics called MaxiGro. The reason I use a hydro nutrient is that in hydro systems, the nutrient has to provide ALL of what the plant needs.
How much fertlizer. If the fertlizer or nutrient has dosage for orchids listed, start with that. You can go up from there. Dont worry about underfeeding at the beginning, you can always increase the dosage. You will also read a lot about Nitrogen PPM (parts per million), and that a lot of folk go for 125ppm of N. Basically, divide 10 by the nitrogen % content of your fertlizer. The number you get is how many teaspoons of fert per gallon to give you 125ppm.
I hope this helps to answer some of your questions. I often refer you to read because it with experince will be your best teacher and a straight shot to success. For a lot of very helpful info, check out
Welcome to First Rays Orchids. Click on the "free information link.
Dave