I'm sorry, I don't have much knowledge on this plant as I've never grown one, but you're right about the sunlight. An East or West window with something infront to diffuse the light is best. The brown edges may also be a sign that the humidity's too low. These plants like some humidity. They also like to be kept somewhat moist, but do let it dry out just a bit between waterings. I also use room temperature water on my plants. It's easier on them as cold/hot water can shock/kill the roots respectively. I would DEFINITELY move it out of that pot with no drainage holes. Drainage holes are an aboslute must must must! You'll know if it needs a bigger pot when you remove it from it's current pot. If there's a mass of roots all curled around the bottom, then it needs a bigger pot, but only move it up an inch or two max. There's slightly different instructions for repotting (putting it back in the same size container) and potting up (putting it in a bigger container). Both are relatively simple once you get the hang of it. What can make it difficult is the plant (large, hanging, delicate...) I'm unsure how difficult this plant is in particular. Hopefully someone else can chime in and help you out some more. Best of luck!

I think I'd have to repot it in order to place it on a pebble tray as it's current ceramic pot has the water catcher built in. And as neat as Wardian cases look, it's definitely not my style and it's a big plant to put in a case--the pot is a 20" pot.

Here are pictures of my plant. Thanks!

Hey Matthew, thnx for the pictures! I actually think this is a soil/overwatering issue. My calathea don't show yellowing for a lack of humidity. It's usually because I have been lifting watering cans once too many. So either you're watering isn't tuned into the plant's needs, or your soil holds moisture for too long.